Tag Archives: battery fuel gauge

Review and analysis of XTAR 3600 mAh 18650 Li-Ion protected battery

Posted on by
5

TL;DR – Yes, the XTAR 3600 mAh protected 18650 battery meets its rated capacity! Just make sure your device can drain down to 2.5 volts.

The 18650 lithium-ion battery, named after its size (1.8 cm diameter and 6.50 cm length), has seen continuous improvements in capacity over the years. Nowadays it’s easy to get capacities in excess of 3000 mAh, with the highest capacity cells reaching and even exceeding 3500 mAh.

The XTAR 3600mAh protected 18650 lithium-ion battery, pictured with its original box.

The XTAR 3600 mAh protected 18650 lithium-ion battery, pictured with its original box.

Earlier this year, XTAR, a Chinese company specializing in batteries and battery accessories, announced the newest and highest-capacity addition to their protected 18650 lineup, boasting an impressive 3600 mAh capacity and aimed towards medium-drain applications like power banks and LED flashlights (sorry vapers, this one’s not for you!). After submitting my name for consideration, I was one of a few people selected to receive some samples for review; considering how much I’ve blogged about lithium-ion batteries on here, it only makes sense to talk even more about them!

FULL DISCLOSURE: XTAR provided these batteries to me at no charge for an independent review. They had no editorial control over this review, I have not been compensated monetarily, and all opinions expressed in this review are my own.

Introduction

XTAR’s new 3600 mAh protected 18650 comes in a discreet box, holding nothing more than the battery itself. Like all protected 18650s, the protection comes in the form of a small PCB (printed circuit board) that is stacked on the negative end of the bare 18650 cell, with a metal strap running up the cell’s body to the positive terminal, where a small “button top” is attached to improve electrical connectivity for spring-loaded battery holders.

Positive and negative terminals of the XTAR 3600mAh protected 18650 battery.

Positive and negative terminals of the XTAR 3600 mAh protected 18650 battery. Note the added length due to the button top on the left, and the protection circuit and protective plate on the right.

I was able to request an official datasheet for the battery, which I have included at the end of my blog post. My main goal with this review is to test the batteries from an objective perspective, using dedicated test equipment rather than in-application testing in devices like flashlights. If I do decide to perform such tests, I’ll add a second part to my review (stay tuned!).

Datasheet specifications

Parameter Value
Cell manufacturer (Unspecified)
Nominal voltage 3.6 V
Nominal capacity 3600 mAh
Minimum capacity 3500 mAh
Discharge cutoff voltage 2.5 V
Cycle life @ 80% capacity At least 300 times
(0.5C charge to 4.2 V, 0.03C taper; 0.5C discharge to 2.5 V)
Size 18.1~18.7 mm diameter
68.3~69.3 mm length
Weight ≤50 g
Internal AC resistance ≤45 mΩ
Standard charge CC 720 mA
CV 4.2 V
Taper 50 mA
Fast charge CC 2500 mA (0.7C)
CV 4.2 V
Taper 36 mA (0.01C)
Standard charge voltage 4.2 V
Standard discharge 720 mA CC to 2.5 V
Continuous discharge current >8.5 A
Overvoltage protection Trip 4.25~4.35 V
Recover 4.0~4.2 V
Undervoltage protection Trip 2.4~2.5 V
Recover 2.8~3.0 V
Overcurrent protection Trip 11~13 A
Working temperature Charging: 0~45 °C
Discharging -20~60 °C

Test 1: EBL TC-X Pro battery analyzer

Initial testing of the batteries was tested using my EBL TC-X Pro 4-bay battery analyzer. The test procedure for the batteries was performed as follows:

  1. Record out-of-box/initial voltage before charging
  2. Run automatic capacity test with programmed 1500 mA charge current to 4.2 V, and fixed 500 mA discharge to 2.75 V (charge -> discharge -> charge); record discharge capacity and reported internal resistance
  3. Run manual discharge test with fixed 500 mA current to 2.75 V; record discharge capacity and reported internal resistance
  4. Run manual charge with 1500 mA charge current to 3.65V/LiFePO4 mode (moderate voltage is best for long-term storage); record charge capacity
Parameter (charge current = 1.5A) Cell 1 (bay 1) Cell 2 (bay 2)
Initial voltage (V) 3.65 3.55
Capacity run 1 (mAh @ 2.75 V end of discharge) 3349 3369
Capacity run 2 (mAh @ 2.75 V end of discharge) 3334 3386
Internal resistance run 1 (mΩ) 54.9 46.9
Internal resistance run 2 (mΩ) 53.4 45.1
Storage capacity (mAh charged to 3.65 V) 1402 1494

The capacity numbers seemed a bit low to me, even for an incomplete discharge to 2.75 volts instead of 2.5 volts. I decided to continue testing with a more accurate (and calibratable) battery fuel gauge board, revealing the true capacity of this battery… and it’s as good as the manufacturer promised!

Test 2: Texas Instruments bq78z100 fuel gauge

After realizing that my dedicated battery analyzer wasn’t quite as accurate as I wanted, I decided to use a battery fuel gauge board that I had more confidence in. I had previously built a board based on the Texas Instruments bq78z100, a dedicated battery management system (BMS) on a chip, aimed at 1S and 2S battery packs. This allowed me to calibrate the voltage and current measurements against my Agilent/Keysight U1253B multimeter and therefore get the most accurate results, as I can also program the bq78z100’s autonomous protection features to provide precise control over the discharge cutoff voltage during testing.

Example of the bq78z100-based fuel gauge board being connected to the XTAR 3600mAh protected 18650 battery. (note: actual setup is different than as pictured)

XTAR 3600 mAh protected 18650 battery connected to the bq78z100-based fuel gauge board. (note: actual setup is different than as pictured)

Using this circuit, I was able to get multiple measurements of the battery’s capacity with the help of a Texas Instruments GDK (Gauge Development Kit) as a charger and adjustable load for some of the capacity tests; and an Arachnid Labs re:load 2 adjustable constant-current load, with some additional forced-air cooling for the higher discharge rates.

I suspect that if I had a more, erm, “professional” setup, I could extract even more capacity from the battery, as additional resistance between the battery and the fuel gauge board will cause a voltage drop and subsequent loss in measured capacity.

Available capacity vs. end-of-discharge voltage

This is one of the most interesting test results, in my opinion. Many 1S/”single-cell” devices can’t take full advantage of modern NMC (nickel-manganese-cobalt) cells whose end-of-discharge voltage is below 3 volts, and the following chart helps quantify how much capacity can be extracted if one stops earlier than that. One advantage of reducing the depth of discharge, however, is that it can extend the battery’s cycle life and reduce the amount of capacity loss it experiences with age. As long as you discharge all the way to 2.5 volts and at a modest rate, the XTAR 3600 mAh battery achieves its rated capacity, and then some!

Chart plotting the XTAR 3600mAh protected 18650's voltage, compared to discharge capacity and discharge rate.

XTAR 3600 mAh protected 18650’s voltage/capacity curves at various discharge rates. (click here for full-size chart)

Discharge Rate Capacity/DoD@ 3.3V
(Rel/Abs)		 Capacity/DoD @ 3.0V
(Rel/Abs)		 Capacity/DoD @ 2.75V
(Rel/Abs)		 Capacity/DoD @ 2.5V
(Rel/Abs)
C/10
(350 mA)		 2616 mAh
72.4%/72.4%		 3357 mAh
92.9%/92.9%		 3539 mAh
97.8%/97.8%		 3613 mAh
100%/100%
C/5
(720 mA)		 2555 mAh
(N/A)/70.7%		 3250 mAh
(N/A)/90.0%		 (No Data) (No Data)
C/2
(1800 mA)		 2310 mAh
67.2%/64.0%		 3076 mAh
89.4%/85.1%		 3338 mAh
97.1%/92.3%		 3438 mAh
100%/95.2%
1C
(3600 mA)		 1995 mAh
57.2%/55.2%		 2874 mAh
82.4%/79.5%		 3330 mAh
95.5%/92.2%		 3486 mAh
100%/96.5%

Note that “relative” and “absolute” percentages correspond to the 2.5 volt discharge values for each row and the C/10 rate, respectively. The curve for the C/5 discharge rate ends early, as that data was collected with my Texas Instruments GDK (Gauge Development Kit), which has a hardcoded discharge cutoff at 2.9 volts. One oddity of the 1C curve is how it actually gets slightly more capacity than the C/2 rate; I suspect this is because the internal resistance of the battery was decreasing due to cell heating, allowing the lithium ions to travel across the cell’s separator more easily. Additionally, the capacity under-reporting issue I was having with the EBL tester is more visible in this chart, since a rough extrapolation would bring the discharge curve at 500 mA around 3550 mAh, which is a fair amount higher than the measured ~3340 mAh. If I have the time to recollect some data, I’ll add it to the chart.

Thermal performance

I don’t have the equipment to test beyond a 1C discharge rate, but even at a C/2 discharge rate I noticed significant heating of the battery; nothing disconcerting but still noteworthy. At 1C, the temperature rose to just over 40 degrees Celsius (104 degrees Fahrenheit) by the end of the discharge cycle – definitely warm to the touch but not burning hot. However, I imagine that a discharge rate at 2C or even higher will result in battery temperatures exceeding 50 degrees Celsius (122 degrees Fahrenheit), hot enough to be uncomfortable to hold. Note that lithium-ion batteries should not be charged if they are warmer than 45 degrees Celsius (113 degrees Fahrenheit).

Chart plotting the XTAR 3600mAh protected 18650's temperature, compared to discharge capacity and discharge rate.

XTAR 3600 mAh protected 18650’s temperature curves at various discharge rates. (click here for full-size chart)

Chemistry analysis

After running the data taken at a C/10 discharge rate through TI’s online tool, GPCCHEM, I was able to get two chemistry IDs that would allow me to get an accurate model of the cells for use in their Impedance Track line of fuel gauges.

Chemistry ID (hex) Chemistry Description Cell match Max DoD error (%) Max Ra deviation ratio
5267 LiMn2O4 (Co,Ni)/carbon, 4.2 V Bak: N18650CP (3350 mAh) 2.3 0.27
5634 LiMn2O4 (Co,Ni)/carbon, 4.2 V NanoGraf: INR-18650-M38A (3800 mAh) 2.72 0.61

Don’t pay too much attention to the details; they are provided for informational purposes only and mainly of use for those that want to use these batteries with TI’s fuel gauge chips. The specific models listed are not a guarantee that these batteries actually are that cell model, but it does confirm that our data is otherwise trustworthy; both listed models are high-capacity cells and use a chemistry system containing nickel, manganese, and cobalt (NMC for short), and such chemistries tend to have a relatively high capacity at the expense of lower terminal voltage (3.6 V nominal, 2.5 V at end of discharge; versus the typical 3.7 V nominal and 3.0 V end of discharge).

Conclusion

After my testing, I can confidently say that XTAR’s 3600 mAh 18650 really does achieve its rated capacity. As long as your target device is capable of discharging to 2.5 volts and at a modest rate, it will be able to get the most out of this battery.

If you want to purchase this battery, you can do so from their online store: https://xtardirect.com/products/18650-3600mah-battery?VariantsId=10393

At the time of writing, XTAR is selling this battery at $11.90 USD for a single battery, or $23.80 USD for a two-pack with carrying case.

Downloads

The datasheet for the battery can be found here: https://www.dropbox.com/s/wibdm2ty6zfa7xo/XTAR%2018650%203600mAh%20Specification.pdf?dl=1

Advertisement

Completed: Self-discharge test of Kentli PH5 1.5V Li-ion AA (Part 6)

Posted on by
7

Looking for the teardown or how well the Kentli PH5 battery performs under load? Click the links to learn more.

It’s finally happened – the self-discharge test of the Kentli PH5 Li-ion AA battery has finally come to an end… and it only took almost 3 years!

 

Kentli PH5 Voltage (Jun 18, 2015 – Apr 29, 2018)
Kentli PH5 State of Charge (Jun 18, 2015 – Apr 29, 2018)

april 29 2018 stats

Kentli PH5 self-discharge test statistics

Self-Discharge Rate

I never anticipated this test would run for so long; although the PH5 did not have a manufacturer-specified self-discharge rate, marketing materials suggested that the batteries had a storage life that was “3-5 times longer than Ni-MH batteries”. Wikipedia states that after one year, normal Ni-MH batteries lose about 50% of their capacity, and low-self-discharge (LSD) Ni-MH batteries lose 15-30%.

Correlating this with the data collected from the Texas Instruments bq27621-G1 fuel gauge, the battery lost 40% of its charge within one year, placing it in between the standard and LSD Ni-MH chemistries. Using Excel’s SLOPE() function, the self-discharge rate was calculated to be 0.10108%/day.

Experimental Improvements

There is some error in State of Charge measurement when using the bq27621 fuel gauge. As it uses the Impedance Track algorithm, open-circuit voltage is used to determine a battery’s state of charge upon gauge initialization. This OCV curve is chemistry-specific, with slightly different formulations requiring different chemistry ID codes. The bq27621 has a fixed Chemistry ID of 0x1202 (LiCoO2/LCO cathode, carbon anode), but experimental data revealed a better-matched Chemistry ID of 0x3107, 0x1224 or 0x0380; the first two chemistries pointed towards a LiMnO4/LMO cathode chemistry which I was somewhat skeptical of, but did not test further.

Using another gauge with a different, programmable Chemistry ID could have led to a straighter SoC curve. This wouldn’t be too difficult to reproduce, as the battery voltage can be fed to the gauge in order to recompute the state of charge. Additionally, the bq27621 has a Terminate Voltage of 3.2 volts (the gauge considers this voltage to be the point in which it reads 0% SoC), which is higher than the battery’s protection voltage of 2.4 volts (granted, there is very little charge difference in this area of the discharge curve).

My test setup was not temperature-controlled; I live in a house without air conditioning and room temperatures can vary from 15 to 35 degrees C (59 to 95 degrees F), depending on the season. However, I doubt that this would have had too much impact on discharge rate, and this would better represent real-life scenarios where a constant temperature may not necessarily be guaranteed.

Finally, this test was performed on a new, uncycled battery. I suspect the discharge rate would be significantly higher on an aged battery that was subject to a lot of charge cycles and day-to-day wear.

Conclusion

This was the longest-running experiment I’ve ever conducted on this blog. The Kentli PH5’s self-discharge rate lasts longer than a standard Ni-MH battery, but a LSD (low-self-discharge) Ni-MH battery would still last longer, albeit with a lower terminal voltage. The battery, when new, should be expected to last almost 3 years without a charge (although there won’t be any charge left by then); it will hold about 60% of its capacity after 1 year of storage.

To download a copy of the self-discharge test data, click here.

Self-discharge test of Kentli PH5 1.5V Li-ion AA (Part 5)

Posted on by
2

It’s amazing – 894 days (and counting) have elapsed since the start of my long-term experiment, documenting the real-world self-discharge behavior of the Kentli 1.5V Li-ion AA battery… and it’s still ongoing! How have things fared so far?

Kentli PH5 Voltage (Jun 18, 2015 – November 28, 2017)
Kentli PH5 State of Charge (Jun 18, 2015 – November 28, 2017)

Surprisingly, even after spending nearly 30 months on the shelf, there is still 12% capacity left. The voltage has dropped from 4.216 to 3.692 volts according to my bq27621 Li-ion fuel gauge; the State of Charge (SoC) has dropped 50% since my last update.

november 28 2017 stats

The linear end date prediction is holding pretty steady, having changed slightly to an estimated 0% charge date somewhere in February 2018.

On that note, I’m impressed by how much attention this little battery has received, even years after my initial review. Every day I see a handful of views checking out the teardown and performance metrics, and there seems to be hardly any sign that this will change anytime soon. To everyone who stops by to check out my blog posts: thank you! 🙂

Self-discharge test of Kentli PH5 1.5V Li-ion AA (Part 4)

Posted on by
3

“It’s been a long time… How have you been?”

It’s been almost a year since I started my discharge test of the Kentli PH5 Li-ion AA battery, and the battery has lost almost 40% of its capacity due to self-discharge.

The discharge curve has gotten a lot less… linear since the last time I posted a self-discharge update. The battery is down to 62% state-of-charge, and its voltage has dropped down to 3.89 volts. Still, there’s a lot of time left until this battery reaches empty… but when?

I’m no statistician, but doing a linear extrapolation in Excel gives an approximate end date of January 2018, and the SLOPE() function in Excel gives me an average drop of 0.111%/day. Of course, this can easily change over the course of this test, but only time will tell…

HDQ Utility version 0.96 now available!

Posted on by
2

Whew, I’ve been working on this version for quite a while. With the helpful feedback of many people that have tried my software, I’ve made a large number of improvements to the software; of course, there are plenty of features that aren’t implemented yet, but are being worked on.

More information about how this utility works can be found here.

Download HDQ Utility v0.96 here: https://www.dropbox.com/s/pf0vszgfei7s8ly/HDQ%20Utility%200.96.zip?dl=0

Updates

  • (Major improvement!) Improved HDQ logging functionality (logs are now saved to a separate file instead of being overwritten).
    • Example: “HDQ Log (2015-10-26 at 19.02.50) – HDQ Utility v0.96.txt”
  • Improved HDQ communication (HDQ breaks no longer require the serial port to be opened more than once, and HDQ no-response timeouts are decreased from 0.5 to 0.3 seconds.
  • Reworded certain error messages for clarity.
    • Example: “Communication error: Cannot read byte from address 0x02 (No response from device).” 
  • Renamed file ‘config.txt’ to ‘Config – COM Port.txt’ for clarity.
  • Improved state-of-health warnings by making them non-modal (they do not require the user to dismiss the message).
  • Added more notifications for unidentified and uninitialized batteries. (Uninitialized batteries are determined by a FULL ACCESS security state, with Impedance Track disabled.)
  • Fixed invalid device name and maximum load current readings for v5.02/sn27545-A4 based batteries (e.g. iPhone 6, 6+…).
  • Added time-to-full readings (for firmware older than v2.24).
  • Improved error-checking for device identification (it will display a notice that the tool may need to be restarted).
  • Updated DingoLib UI library to auto-resize window to 0.9x display resolution for improved readability on larger monitors.

To-Do

  • Create a dedicated section on my blog for the HDQ Utility.
  • Create a user’s manual describing the parameters displayed by the program (in particular, the Advanced Battery Information section).
  • Improve data logging functionality by saving logs to a subdirectory instead of the program’s root to decrease file clutter.
  • Improve error-checking for commands (retry reads if one or more bytes are not received from the device).
  • Add error statistics indicating how many communication errors occurred during data collection.
  • Improve support for older (older than v1.25) firmware.
  • Improve support for v5.02/sn27545-A4 devices (make use of advanced commands available in this firmware version).
  • Add support for restarting of data collection without having to re-execute the program.
  • Add Data Flash memory functions to allow for readout of advanced configuration, serial number, lifetime/black-box data, etc.
  • Rewrite this program in something that’s not LabWindows/CVI… also, use of a GUI rather than a non-console text UI.

Self-discharge test of Kentli PH5 1.5V Li-ion AA (Part 3)

Posted on by
4

Aw what, it’s October already? So much for having another blog post in September…
But anyway, “more months, more data!™”

The voltage of the PH5 has dropped down to 4.093 volts as of today (October 1st, 2015), and its State of Charge is now 93%. There’s just enough data to guess the discharge rate of the PH5: with the currently logged data, the PH5 self discharges at approximately 0.103%/day. At this rate, the cell should last years before finally reaching zero. Looks like this will be a very, very long term test…

(At least that would give me more time to procrastinate write blog posts.)

Self-discharge test of Kentli PH5 1.5V Li-ion AA (Part 2)

Posted on by
1

After my first self-discharge analysis of the Kentli PH5 Li-ion AA battery, I have collected another month’s worth of data.

The battery’s voltage drop has been surprisingly linear. Although I didn’t get the exact day when the bq27621-G1’s State of Charge readout dropped to 99%, it is quite clear that the state of charge is dropping with a fairly steep curve now. That said, because the battery’s voltage is still far away from the ‘flat region’ of the discharge curve, it is difficult to determine when the battery will discharge itself completely at this time.

Self-discharge test of Kentli PH5 1.5V Li-ion AA (Part 1)

Posted on by
4

As an extension to my previous performance analysis of Kentli’s PH5 Li-ion AA battery, I fully charged an unused PH5 and left it on my desk to self-discharge. Every now and then, a Texas Instruments bq27621-G1 fuel gauge is hooked up to the Li-ion battery terminals (in the case of the PH5, the recessed ring around the 1.5V terminal) and the bq27621’s default settings are used to measure the voltage and state of charge.

I started this test on June 18th, 2015 and will keep taking occasional measurements until the protection IC in the PH5 shuts down.

Since the 18th, the voltage dropped from 4.216 volts down to 4.192 volts as of July 6, 2015; the bq27621’s State of Charge reading remains at 100% for the time being. The voltage drop has been fairly linear so far, but I expect it to taper off as the battery discharges to the Li-ion cell’s “flat region”, and only after that do I expect the cell’s voltage to decline more rapidly.

So, about that Kentli battery…

Posted on by
7

It’s been a while since I’ve posted about the Kentli PH5 battery, which is a Li-ion cell with an integrated 1.5-volt regulator, wrapped up in an AA-sized package. Although I haven’t written much about its performance yet, that doesn’t mean I haven’t been doing work on it. In fact, I’m sure I have never put so much work into a single blog post before!

The full analysis of the battery’s performance is not fully complete, but I’ll reveal some details of my test setup and what I’m currently working on:

Analysis

I’m doing a much more thorough analysis of this battery than I have done with any other one on this blog. I have created a second bq27541 fuel gauge board, but with the explicit goal of measuring the voltage, current, passed charge (mAh) and temperature of a given DC-DC converter. This way, I can measure the input and output of the DC-DC converter simultaneously, greatly enhancing the data I can collect.

These are the data points/attributes I am currently collecting:

  • Battery voltage sag at high load currents
  • Battery capacity over different load currents (it’s not constant!)
  • DC-DC efficiency, both at different load currents but also over a single discharge cycle
  • Temperature rise of the DC-DC converter at different loads, and also over a single discharge cycle
  • Changes in battery capacity and internal resistance over many charge cycles

I want to be as thorough as possible with my measurements, mostly because nobody else has done a detailed performance review of this rather unusual battery, but also partially because I want to challenge myself and see how much of a “real engineer” I can be (#JustHobbyistThings). 😛

Looking inside a (fake) iPhone 5S battery

Posted on by
18

Considering how popular the iPhone is, there’s always going to be some counterfeits out there. I’ve been out buying various iPhone batteries to build a database of each generation’s characteristics, but one model has eluded me so far: the iPhone 5S. The iPhone 5C’s battery that I bought appears to be genuine (but with its own issues), but none of the iPhone 5S batteries I’ve bought so far (4 of them at the time of writing this blog post) were genuine. All of these fakes look like a genuine battery at first glance, but all of them share a few common traits.

Battery teardown

The fake battery sports the usual iPhone battery information, complete with some dot-matrix printed data and a data-matrix barcode. It’s labeled with a capacity of 1560 mAh and 3.8 volts nominal voltage.

Comparison between real and fake iPhone 5S battery

Comparison between real and fake iPhone 5S battery

The connector itself has two points for soldering the connector to provide durability. However, with the fake batteries, they are not soldered down. The two spots on the ends of the connectors are dark with a small point visible inside it (that point is the reinforcement pin on the connector). If this connector is installed in an iPhone, it will probably not come out without either damaging the battery’s connector, or worse, leave the plastic connector piece inside the phone, requiring tweezers to remove.

Connector lifted off with a hobby knife

Connector lifted off with a hobby knife

iPhone 5S and 5C battery pinout

iPhone 5S and 5C battery pinout

Removing the black protective tape reveals an iPhone 4 battery fuel gauge board. The connector is soldered to this board, with four solder points visible.

iPhone 4 battery PCB with soldered-on flat flex connector

iPhone 4 battery PCB with soldered-on flat flex connector

Pulling out the PCB  reveals another characteristic of these fake batteries: the positive terminal is cut short, with another metal section being clumsily spot-welded to the stub on the cell.

Note how the battery tab is poorly welded to the PCB.

Note how the battery tab is poorly welded to the PCB.

Battery fuel gauge data

The battery fuel gauge requires proper programming to accurately indicate the battery’s charge status. Because of this, each iPhone battery generation has its own specific configuration.

The fake iPhone battery retains the programming for the iPhone 4’s battery, which is a designed capacity of 1420 mAh, using a bq27541 fuel gauge running version 1.25 firmware. The data inside it is often that of a used/recycled battery as well.

This data can be (partially) read out directly from the iPhone with a tool such as iBackupBot, but more data can be read if the battery is read with another tool. I have the EV2400 from Texas Instruments to read this out on a PC, but this data can be read out with a USB-to-TTL serial port, a logic gate (a logic inverter) and a small MOSFET transistor.

I created a small tool that uses this circuit to interface with the fuel gauge and read out its data. Check it out here.

Using my tool, this is the report for one of these fake batteries. Note how it is identified as an iPhone 4 battery. Don’t be fooled by the calculated state of health. It’s not accurate for this battery as the fuel gauge still thinks it’s still inside an iPhone 4 battery pack.


**** START OF HDQ BATTERY LOG REPORT ****
HDQ Gas Gauge Readout Tool version 0.9 by Jason Gin
Date: 9/30/2014
Time: 0:52:24
Serial port: COM26

Battery Identification
========================
DEVICE_TYPE = 0x0541, FW_VERSION = 0x0125, DESIGN_CAPACITY = 1420 mAh
Battery's configuration matches that of a standard iPhone 4 battery.

Basic Battery Information
===========================
Device = bq27541 v.1.25, hardware rev. 0x00B5, data-flash rev. 0x0000
Voltage = 3804 mV
Current = 0 mA
Power = 0 mW
State of charge = 45%
Reported state of health = 0%
Calculated state of health = 99.3%
Cycle count = 14 times
Time to empty = N/A (not discharging)
Temperature = 27.9 °C (80.3 °F) (3009 raw)
Designed capacity = 1420 mAh
Heavy load capacity = 628/1410 mAh
Light load capacity = 673/1455 mAh

Advanced Battery Information
==============================
Capacity discharged = 0 mAh
Depth of discharge at last OCV update = ~778 mAh (8768 raw)
Maximum load current = -200 mA
Impedance Track chemistry ID = 0x0163
Reset count = 11 times

Flags = 0x0180
Flag interpretation:
* Fast charging allowed
* Good OCV measurement taken
* Not discharging

Control Status = 0x6219
Control Status interpretation:
* SEALED security state
* SLEEP power mode
* Constant-power gauging
* Qmax update voltage NOT OK (Or in relax mode)
* Impedance Track enabled

Pack Configuration = 0x8931
Pack Configuration interpretation:
* No-load reserve capacity compensation enabled
* IWAKE, RSNS1, RSNS0 = 0x1
* SLEEP mode enabled
* Remaining Capacity is forced to Full Charge Capacity at end of charge
* Temperature sensor: External thermistor

Device name length = 7 bytes
Device name: bq27541

**** END OF HDQ BATTERY LOG REPORT ****

Reading out HDQ-equipped battery fuel gauges with a serial port

Posted on by
78

Battery fuel gauges are the unsung hero of the battery world. There’s more to it than just measuring the voltage on the battery terminals,. These little chips are microcontrollers (tiny computers, essentially) that sit inside the battery pack and keep tabs on the battery’s performance for the life of that battery pack.

Texas Instruments makes battery fuel gauges that are small enough to fit in the circuitry of a cell phone, and one of the most common ones that uses this technology are iPhone batteries. These batteries use a single-wire interface called HDQ (which stands for High-Speed Data Queue). It may sound similar to Dallas Semiconductors’ 1-Wire protocol, but the two are completely different and incompatible with each other.

Protocol details

The HDQ protocol can be emulated with a serial port and a little bit of external circuitry. The protocol can be emulated with a serial port at 57600 baud with 8 data bits, no parity bit and 2 stop bits. Because this is a bi-directional bus, an open-drain configuration is needed. Most TTL serial ports are not open-drain, so some circuitry is required to do this. TI’s application note suggests using a CMOS inverter and an N-channel MOSFET along with a 1 kOhm pull-up resistor, but this can be cut down with a 74HC07 open-drain buffer and pull-up resistor.

[EDIT: June 13, 2015 – Corrected schematic]

The HDQ protocol uses a short pulse to indicate a logic 1, with a longer pulse to indicate a logic 0. The data is sent LSB (least significant byte) first, with a 7-bit address and an eighth bit to indicate if the operation is a read or write (0 is read, 1 is write). If it is a read operation, the fuel gauge will respond with one byte of data. As you might think, this is a very slow means of communication; the typical bus speed is 5-7 kilobits per second, but the actual usable throughput will be less than this.

The hack in this is that the bit timing can be made by sending a specially crafted UART byte that meets the timing specifications. Each bit takes up one byte of UART buffer memory, with 24 bytes being enough to perform an HDQ read (the first 8 bytes are echoed back to the PC and need to be ignored by the software). TI’s application note goes into this with a bit more detail.

Windows HDQ utility

HDQ utility icon, in all its pixelated glory.

HDQ utility icon, in all its pixelated glory.

I have written a small Windows program that will read out the battery’s main data, identify as a certain iPhone battery model (most iPhone batteries are supported), and save a copy of this data to a text file for safekeeping. This program requires the National Instruments LabWindows/CVI Runtime library to run, since I whipped this program up with the first available IDE on my college PC.

fdd82eef8d

Screenshot of HDQ Utility version 0.96

The source code is not yet available (translation: I’m too ashamed of my programming skills to share it with others); however, a Windows executable is available for download below.

You will need to download the National Instruments LabWindows/CVI Runtime to run this program.

Current version (0.96): https://www.dropbox.com/s/pf0vszgfei7s8ly/HDQ%20Utility%200.96.zip?dl=0

Version 0.95: https://www.dropbox.com/s/7xdurbh9qibdftl/HDQ%20Utility%200.95.zip?dl=0
Version 0.9: https://www.dropbox.com/s/cd3esa5us6elfgr/HDQ%20Utility.zip?dl=0

Contributions are always accepted! Email me if you would like to send in a battery for me to analyze, or you can buy me a coffee through PayPal:


[EDIT – July 28, 2016] Welp, looks like the PayPal button’s broken (or was it never working to begin with…?). If you’d like to send anything to me, just give me a shout at ginbot86@gmail.com!

[EDIT – August 2, 2016] Whoops, looks like I never had the button working in the first place. Hopefully it works this time.

 

So Phone Me Maybe: A list of iPhone/iPad batteries with gas gauge functionality

Posted on by
43

Looking for my HDQ Utility to read out your own batteries? Click here!

UPDATE: Turns out the iPhone 3G and 3GS do have gas gauges! I will add them to my list as I find out more about them.

Each iPhone generation since the iPhone 4 iPhone 3G uses a TI gas gauge and uses the HDQ bus (iOS refers to this as the SWI [single-wire interface]) to communicate with the outside world. For more information about the HDQ protocol, click here.

I’ve noticed that many of the iPhone 5S and 5C batteries that can be purchased online are reusing iPhone 4 circuits, which will cause a significant decrease in gauge accuracy (proper parameters need to be programmed into the gas gauge, and that information is chemistry dependent), and the protection circuits in the iPhone 4 battery PCB will kick into overvoltage protection mode at 4.25 volts, less than the 4.3 volts that the iPhone 5 (and newer) batteries need to charge fully.

Because I have been unable to find a list of information of each battery generation, I’m making one myself. Because nobody else has dug this deep into the fuel gauges that the iPhone uses, I have to get this information experimentally (that is, by buying various batteries from online shops; the iPhone 5S battery has been very difficult to get, besides the fake ones I mentioned earlier).

So far I’m in need of an iPhone 3G (not the 3GS) battery, as well as all iPad batteries (or, if you have my program on hand, what model the battery is intended for, the fuel gauge device (eg. bq27541, bq27545), firmware version and designed capacity.

Model Gas Gauge Firmware Designed Capacity Default Unseal Key? Comments
iPhone 3G bq27541 ? ? Yes (0x36720414) Need to acquire one of these.
iPhone 3GS bq27541 1.17 1200 mAh Yes (0x36720414) Limited feature set. My utility will throw “No response” errors when reading this battery.
iPhone 4 bq27541 1.25 1420 mAh Yes (0x36720414)
iPhone 4S bq27541 1.35 1430 mAh Yes (0x36720414)
iPhone 5 bq27545 3.10 1430 mAh No (0x52695035) Many thanks to Yann B. for finding the unseal key!
iPhone 5S bq27545 3.10 1550 mAh No (0x84966864)
iPhone 5C bq27545 3.10 1500 mAh No (0x84966864)
iPhone 6 sn27545-A4 (note 4) 5.02 1751 mAh No (0x65441236)
iPhone 6 Plus sn27545-A4 (note 4) 5.02 2855 mAh No (0x18794977)
iPhone 6S sn27546-A5 (note 5) 6.01 1690 mAh No (0x90375994)
iPhone 6S Plus sn27546-A5 (note 5) 6.01 2725 mAh No (0x11022669)
iPhone SE Unrecognized (note 6, 7) (A1141/0x1141) 1.03 1560 mAh No (unknown) (See note 6)
Apple Watch (38mm) sn27545-A4 5.02 235 mAh No (0x09130978)
Apple Watch (42mm) sn27545-A4 5.02 245 mAh No (unknown) If anyone has one that reads “FULL ACCESS” in my program, please send it to me! 🙂
iPad (3rd gen) bq27541 1.35 11560 mAh Yes (0x36720414)

Notes:

  1. All known iPhone battery models use custom firmware, so not all of the features that the mainstream gas gauge models use are available. For example, none of these gauges will calculate the battery’s State of Health percentage (it is basically the percentage of the battery’s full charge capacity (it degrades with use) versus its designed capacity.
  2. The iPhone 5C’s battery label indicates a designed capacity of 1510 mAh, but the battery I’ve received indicates a capacity of 1550 mAh. As I have only been able to get one of these batteries that seem to be genuine, I will need to get more batteries of this type to confirm that this information is correct.
  3. The iPhone 5’s battery label indicates a designed capacity of 1440 mAh, but the fuel gauge reports 1430 mAh. The 5S battery reports 1550 mAh, but is labeled 1560 mAh. The 5C reports 1500 mAh, but is labeled 1510 mAh.
  4. The iPhone 6 and 6 Plus use a special firmware that is identified in TI’s battery software (except the very latest releases where such data was removed), and it has a very extensive feature set, and a lot of data logging features.
  5. The iPhone 6S/6S Plus use a firmware version similar to the iPhone 6/6 Plus, but with a newer chip and some features trimmed out. I’m reasonably confident that the chip is an sn27546-A5 but have no idea if it’s the official part designator.
  6. The iPhone SE battery seems to have a unique custom chip, but has gone back to a DFN-based package (similar to bq27541) rather than a BGA like the bq27545/546. It is marked “A1141” and does not respond to my HDQ adapter, only the official TI EV2300/EV2400. I have only one in my possession, so I am not 100% sure whether this is true for this series of batteries.
  7. Come to think of it, I might have been ripped off with the battery I received, and it could very well be that I just have a counterfeit that uses a non-TI gauge.

Looking inside an iPhone 4/4S battery

Posted on by
30

A classmate of mine had a couple broken iPhones that he ‘relieved’ of their batteries and let me take a look at them. Being the curious type I peeled away the outer layers of tape to reveal the protection circuit. I spotted a current sense resistor, and  that got me thinking…

… can it be? Yes, I found a bq27541 fuel gauge chip inside the battery! After fooling around with the battery, I found out that the battery is using the HDQ interface.

iphone battery pinoutThe HDQ bus, which stands for ‘High-speed Data Queue’, is a single-wire communications bus used by TI fuel gauges. It’s similar to Maxim’s 1-Wire protocol but runs with different protocols and timing. It operates at 7 kilobits per second (so much for ‘high speed’ right? 😛 ) and a refresh of the data memory in the TI software can take almost half a minute. However, it’s good enough for occasional polling (like every minute or so) since it’s unlikely that the gauge will be read from every second.

The bq27541(labeled BQ 7541) in the iPhone battery runs an unusual firmware version. It’s running version 1.35 and doesn’t match with any release on TI’s website. The gas gauge is sealed so initially it seems like gaining access to the Data Flash memory would be impossible. However, in non-Apple fashion, the gauge’s passwords are left at the default; 0x36720414 and 0xFFFFFFFF for the unseal and full-access keys, respectively (and it’s not the first time Apple’s done this!). Since the firmware version is unknown, I told bqEVSW to treat the chip as if it were the bq27541-V200. I then saved only the calibration, capacity, resistance and lifetime data.

Updating the firmware over HDQ was a nightmare. It took over a dozen tries for each of the two batteries I had, and the update process took 45 minutes (!) to update the bq27541 to the V200 firmware. At one point, it seemed as if I bricked the chip, but a power-on reset of the chip by shorting the cell very quickly 😀 sent the device into ROM mode (ie. firmware-update mode). From there I used bqCONFIG to update the firmware, and it was successful! Now I could use GaugeStudio to interface with the gauge rather than the unsightly bqEVSW software.

bq27541 updated to version 2.00

bq27541 updated to version 2.00

Given how long it took for me to update the firmware of the gauge, I have doubts that iPhones will update their batteries’ firmware in-system. Hell, the iPhone OS ignores the bq27541’s State of Charge readings and substitutes its own. Nice going, Apple!

Now to start going through cell phone recycling bins to pull out dead iPhone batteries for their gauges…

Tearing down and analyzing a cheap-ass “Xtreme” $3.50 external phone battery

Posted on by
1

I was shopping around at this electronics liquidation store and stumbled upon a couple cheap buys: A “1900 mAh” external phone battery and another 4400 mAh pack (which will be the subject of another post and teardown). The batteries were originally priced at $7 and $38 respectively, but they were on sale at half price. For $3.50, I was curious enough about the 1900 mAh battery’s real capacity that I bought it anyway, expecting to be disappointed.

The pack itself is roughly half the size of a typical smartphone and about 1.5 times thicker. The casing itself has no screws; the manufacturer decided it was too expensive to use screws so they simply ultrasonic-welded the case shut. After about half an hour with a plastic spudger tool, I was able to crack the case open.

2014-01-05 00.11.26The soldering quality, surprisingly, is pretty good for a sub-$10 device, save for a bunch of hand-soldered components with flux residue left behind. The circuit board is made up of a battery protection circuit (yes, they actually put one in!), an ME2108A-50 boost converter,  something I’d assume to be a charging circuit, and an LM324 op-amp as a “gas gauge” (if you could even call it that!).

2014-01-05 00.11.36The cell appears to be a thicker version of a typical cell phone battery. It’s similar in size to something like a Nokia BL-5C which is a 1020 mAh cell, and is 5.6 mm thick. The cell in the charger is 7.7 mm thick. The charger’s cell is only 37.5% thicker but should have 190% of the capacity… yeah, no. This is not going to be very promising, given how the spot-welded nickel strips literally fell off the cell when I tried to desolder it from the PCB.

After soldering some 20-gauge solid wire to the terminals and hooking it up to a bq27425-G2A fuel gauge chip, I noticed that it reported that the fully-charged voltage is 4.25 volts. This charger tries to squeeze the most out of the cell by overcharging it! Granted, a Li-Ion cell’s maximum terminal voltage is 4.25 volts but it shouldn’t settle down to this voltage after charging!

1900 mah charger overvoltageAfter performing a few learning cycles to determine capacity and resistance, the cell holds merely 1370 mAh. The internal resistance is about 85 milliohms, which tells me that at least they used a relatively fresh cell in this charger and not just some recycled cell (*cough* UltraFire *cough*).

1900 mah charger graphI knew from the get-go that this battery was going to be a let-down, and I was right. But hey, for $3.50 I get a half-decent 1370 mAh cell and a few scrap chips (no way I’m reusing that battery’s PCB as-is!). But my verdict: Avoid this battery pack if you intend to use it to, I dunno, charge your phone. 😛

Skin-Deep Authenticity: Tearing down a “genuine fake” Samsung Galaxy S II battery

Posted on by
4

When you have the same smartphone for almost 3 years, it’s likely that your original battery’s not going to last as long as the service contract. And as long as you’re not an iPhone user you will probably look into a replacement or spare battery.

coverMy first replacement cell was a 2-pack of “1800 mAh” batteries for $5. These had 66% of the stated capacity and TI’s Impedance Track gauge said that the DC internal resistance was about 250 milliOhms. That’s… pretty terrible. Those two cells quickly led their end in a battery recycling bin. My next two were “genuine” cells from eBay. They cost about $12 each and had rather authentic-looking labels on them too. Their performance was pretty good, but one of them became all bloated so I decided I’d take a look at the cell that’s inside. I peeled off the label, and the truth comes out…

2014-01-01 04.53.39This battery was an outright lie in terms of capacity! 1350 mAh is about 80% of the 1650 mAh capacity that was written on the outer label. The cell’s manufacturer is unknown, but the battery markings read “BMW-524655AR 1350mAh 2012.09.03.1110”. Wait, look at that manufacturer date. Something’s fishy…

2014-01-01 04.53.54The outer label states a manufacture date of July 20, 2012. The internal cell states one of September 3, 2012. Unless this battery was manufactured in a time-bending factory, then these batteries certainly aren’t genuine.

Next up was the protection circuit. The “genuine fake” battery uses a DW01 protection IC and uses a generic 8205A dual NFET for swiching. And there wasn’t even a thermistor; the PCB uses a 1.5k ohm resistor to simulate one. A genuine board uses a single SMD package that integrates the FETs and the protection IC.

Below is a comparison of the protection board of a fake battery and a “genuine fake” one. At least the “genuine fake” uses the same black appearance of the original.

The “genuine fake” battery, after only 2 months of usage (not even 20 charge cycles’ worth), became so swollen that I can’t keep the back cover on. Running this battery through a bq27425-G2A battery gas gauge determined that the real capacity of the battery is a paltry 944 mAh, with an average internal resistance of 187 milliOhms. Absolutely pathetic.

samsung galaxy s ii replacement battery old ra graphGoes to show you get what you pay for. But some things may be more deceiving than others…

Convenient chips, inconvenient packages: Making use of the Texas Instruments bq27421-G1 lithium-ion battery fuel gauge chip

Posted on by
9

As seen on Hackaday!

I ordered some sample chips from TI a few weeks ago, most of them being lithium-ion battery “fuel gauge” chips. These chips are used in electronic devices to determine exactly how much energy is in the battery, and if the chip’s sophisticated enough, provide a “time until empty” prediction.

The bq27421 from TI is packaged in a tiny 9-ball grid array, packaged as a wafer-level chip scale package (WLCSP). This means there is no epoxy covering like normal ICs, making for a compact design that’s a good thing for space-constrained applications like modern cell phones. I’ll talk about this chip later on in this post.

The tiny BGA package means that prototyping with these chips is difficult if not impossible, depending on how large the chip is that you’re working with. The bq27421 is about 1.6 mm x 1.6 mm, which is less than 1/3 of the size of a grain of rice. No way you’d be able to put that on a breadboard… right?

2013-06-14 15.51.58Well, you can, with a small breakout board, some magnet wire, epoxy (a bigger deal than you might initially think), patience and steady hands. I mounted the chips in what I call a mix between dead-bug (where the contacts face up as if the chip was like a dead bug on the ground) and chip-on-board construction (where the chip is glued directly to a board, wire-bonded and then covered in epoxy). I used some SOIC-to-DIP boards from DipMicro Electronics (link). I often use these boards when doing work on prototyping board since using these surface-mount parts reduce the board’s height compared to using actual DIP packaged chips (which are much less common for modern ICs anyway).

The chip is first affixed to the breakout board using a small amount of epoxy and allowed to cure for several hours. The epoxy, from what I’ve found, is crucial to your success; superglue and other adhesives won’t stand up to the heat of a soldering iron, and if it loosens you can end up ruining your chip and wasting your time spent working on it.

After letting the epoxy cure, I then prepare the bond pads around the chip. I place a liberal amount of solder on each pad to allow easy connection with the iron later; I want to minimize the stress on the tiny 40-gauge magnet wire because once the connection is made, the solder ball that the chip came with won’t be as easy to solder to the second time around.

Next up is the actual soldering process. I created a pinout for the board in PowerPoint to help plan out how I’ll solder the wires. After tinning a long length of 40-gauge magnet wire, I then solder the wire first to the solder ball on the chip, then solder the other end to the pad I previously put solder on. To minimize the stress on the wire afterwards, I use a small utility knife to cut the end of the wire where the pad is. I then complete this for the rest of the contacts. This took me an hour and a half the first try, but took me about 20 minutes the second time around. Also, for my second try, for the BAT and SRX pins, which carry the full current for any loads connected, I used 30-gauge wire-wrapping wire to allow a bit more current-carrying capacity. It probably is overkill since the maximum current rating for the bq27421 is 2 amps continuous, but I felt a bit more at ease connecting the pins this way.

After checking for short and open circuits with a multimeter I then placed headers onto the board and put it into my “evaluation board” that I created just for this chip. Using an EV2400 box from TI, used to connect to their vast range of battery-management chips, I connect the box to my PC and run their GaugeStudio software to verify that the chip works.

… and it does, like a charm! I was able to communicate with the chip and also view its operation in real-time.

One thing that was causing me trouble before was that after removing the battery and putting another one in, I found that the gauge chip sometimes wouldn’t be recognized by the PC. Being unsure why it was doing this, I dug through the reference manual, and found one tiny part in the manual that showed me why it wasn’t working consistently.

gpoutThe GPOUT pin was left floating on my board, and the chip requires a logic high signal before it starts up. This brings back memories of my digital electronics class in college; these floating inputs can cause all sorts of trouble if you’re not careful, and in this case, it was mentioned only once in the reference manual. After using a 1 megohm resistor to pull up the pin, the chip worked flawlessly. Now that I verified that the chip was working, I mixed up some more epoxy and covered the chip, making sure that the bond wires and chip were covered to prevent damage.

After all that, I had a couple working highly-advanced battery gauges that I could fool around with, and also learned a couple things about deadbugging SMT components and also the basics of chip-on-board construction.