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!
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?
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.
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! 🙂
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…
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
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…
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.
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.
In my previous blog post, I tore down the Kentli PH5 battery – a Li-ion battery that has an internal 1.5-volt regulator that allows for terrific voltage stability… up to a point. In terms of data collection, so far I have collected 55+ runs of data logs (248 MB of text files!) and still do not quite have all the data I want. As for the data that I do have, I will be disseminating them with as much thoroughness as possible.
Updated (May 1, 2018):
The battery’s self-discharge rate experiment has come to its conclusion – click here to read it.
I forgot to add a diagram of my test setup – here’s a Visio diagram of the hardware used to test the battery’s performance… Click here to see the full-sized diagram.
Voltage vs. load current
As expected, the voltage output of the PH5 remains quite stable, up until roughly 2.1 amps where the voltage sags noticeably until the regulator goes into overcurrent protection mode.
A maximum load capacity of 2.1 amps seems to be a bit… limiting. That said, I have not done tests on the PH5’s transient load capacity, as it would require more automated control than what I currently have available.
Another issue with having such a flat discharge curve is that any device that performs fuel gauging using voltage alone will report 100% capacity, until it suddenly shuts down. This could be a big problem for digital camera users, as they will have no indication that their batteries are running low, until the device abruptly stops working. If the camera was writing an image to its memory card when the battery died, it could cause the image to be corrupted, or worse, damage the file system on the card!
Voltage vs. state-of-charge
Unless you are running the battery at a high discharge rate, the output voltage will be flat at 1.5 volts before abruptly brickwalling and dropping to zero immediately at the end of discharge. At a high load (in the case of the graph below, at 2 amps), the voltage remains flat until the very end of the discharge cycle (99% depth of discharge for my test run), where it quickly tapers off and drops to zero.
Capacity vs. load
This is the big one, and it took a lot of work to get this data, especially at low loads (48+ hours of continuous logging is just asking for Murphy’s Law to come into play). I used almost 50 discharge runs to create the graph below.
This is where things get… interesting. I was expecting the capacity to peak at low currents then taper off as the load current increases. Instead, I noticed a definite ‘hump’ in capacity around the 250 mA mark (reaching a maximum of 1700 mAh / 2550 mWh), and only after that point did I see the expected downward slope in capacity, reaching 1200 mAh (1800 mWh) at the 2 amp mark.
This data brings forth some very interesting conclusions. The PH5’s capacity is inferior to its Ni-MH counterparts (even the relatively crappy ones), and at higher discharge rates it has similar capacity to that of an alkaline at the same load, albeit with much better voltage stability than the Ni-MH or alkaline chemistries.
Although I won’t go into too much detail for the next few points (I haven’t gotten quite enough data to be presentable), there are some other issues with the battery that I think should still be mentioned.
One issue is the amount of heat the battery gives off at high loads. At 2.1 amps, I had to use a fan to blow cool air onto the DC-DC converter just to prevent it from entering its over-temperature shutdown mode. Although the converter itself can tolerate elevated temperatures, the Li-ion cell inside will not; the uneven heating that the cell will encounter could potentially degrade its lifespan in the long run.
Another problem is efficiency. At 1 amp, the DC-DC converter is about 75% efficient, and is only 65% efficient at 2 amps. I have not tested the converter’s efficiency at lower loads yet, but I doubt it will achieve more than 85-90% efficiency.
A potential issue with this battery is self-discharge. The buck converter remains active all the time, unless the converter or the Li-ion protection circuit enters a protective shutdown state.
I have not had a chance to fully charge an unmodified battery in order to perform a long-term self-discharge test, but I will create another blog post for that, if/when the time comes. Update (May 3, 2018): See the top of the page for the link to the self-discharge test results.
Overall, I’m on the fence when it comes to this battery. Its innovative design does provide unparalleled voltage stability, but its low capacity even at moderate discharge rates dampens the fun significantly. Additionally, the 2.1 amp discharge limit could prove to be a bottleneck for some high-drain applications; this, coupled with the cell’s tendency to shut down abruptly when the internal cell runs empty could potentially cause file system corruption for digital cameras that have not been designed to handle such sudden power interruptions.
Also, the batteries are very costly. At about $10 per cell, you may want to think twice about replacing all your current disposable and rechargeable batteries with these newfangled Li-ion ones. Don’t forget the charger either, as a special charger is required to make contact with a recessed terminal on the top of the battery.
Overall, this cell is… interesting. Just don’t expect a miracle in a steel can.
Bottom Line: This is a niche product and should not be considered a universal replacement for alkaline or Ni-MH AA batteries.
It Glows when it Blows™! [add obligatory Michael Scott line here]
Okay, now that the lowbrow humor has been dealt with, I had to replace a car fuse because of a shorted 12-volt power socket. Luckily, I was able to replace the fuse without the circuit blowing again; however, I had used the only spare fuse in the fuse box and needed to buy some more in case the fault was to recur. Browsing my local Canadian Tire, I stumbled upon a pack of fuses that allowed for a visual check for blown fuses by simply turning on the ignition: the Littelfuse Smart Glow fuse. A 36-pack of these fuses cost about $35 Canadian, making them a bit pricier than their non-illuminated counterparts.
The Smart Glow fuse is comprised of three main components: the actual fuse (which is really just a regular automotive fuse), a 360-ohm resistor, and a dual red LED package with the diodes in inverse parallel to allow for the fuse to glow regardless of orientation. The LEDs and resistors are affixed to the fuse body using various epoxies: an opaque red epoxy to glue the components down, a conductive silver-filled epoxy to provide an electrical connection without soldering, and a clear epoxy to protect the components from damage; the fuse amperage is re-printed on top of the protective epoxy coating since the resistor and LED obscure the original fuse’s markings.
Simply put, this acts like any other automotive fuse would. The only difference is that the LED will illuminate if the fuse is blown, and sufficient load is still present in the circuit to provide enough current for the LED to act as a fault indicator.
When testing the fuse’s brightness, I found it to be quite noticeable at 5 volts and almost blindingly bright when run at 14.4 volts (the approximate charging voltage for a 12-volt car battery).
Running this circuit through a simulator, the LED has almost 35 mA of current running through it. Given how LEDs are typically rated for a maximum of 20 mA, this LED is not going to last long; that said, it shouldn’t need to run for a long time as the LED’s only purpose is to notify the user that the fuse needs to be replaced (and at that point the fuse and its indicator will be disposed of anyway).
Yes, it glows when it blows; I have nothing more to add.
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:
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:
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). 😛
June 17, 2015 – Performance analysis/review HERE!
After having an entire month of dormancy on this blog, I’m finally beginning to cross off the blog posts on my “Pending” list.
Last year, I made a blog post talking about Kentli’s lithium-ion based AA battery that has an internal 1.5 volt regulator. The first order never arrived, and the second one had arrived a few months ago but I never got to actually taking one of the cells apart. That changes today.
The battery itself looks like a regular AA battery, except for the top positive terminal. There’s the familiar ‘nub’ that constitutes the 1.5 volt output, but also has a recessed ring around it that provides a direct connection to the Li-ion cell’s positive connection for charging.
After peeling the label, we are met with a plain steel case, save for the end cap that appears to be laser spot-welded. Wanting to take apart the cell with minimal risk of shorting something out inside, I used a small pipe cutter to gently break apart the welded seam. Two revolutions and a satisfying pop sound later, the battery’s guts are revealed.
The PCB that holds the 1.5 volt regulator is inside the end cap, with the rest made up of the Li-ion cell itself. Curiously enough, the cell inside is labeled “PE13430 14F16 2.66wh” which is interesting in more than one way. First of all, the rated energy content of the cell is less than what’s on the outside label (2.66 watt-hours versus 2.8), and the cell inside is actually a Li-ion polymer (sometimes called a “Li-Po” cell) type; I was expecting a standard cylindrical cell inside. Unfortunately, my Google-fu was unable to pull up any data on the cell. I might attempt to do a chemistry identification cycle on the cell and see if TI’s battery database can bring something up.
The end cap’s PCB uses a Xysemi XM5232 2.5 A, 1.5 MHz synchronous buck converter to provide the 1.5 volt output. According to the datasheet, it is a fully integrated converter with all the power semiconductor components residing on the chip itself. The converter is rated for 2.5-5.5 volt operation, well within the range of a Li-ion cell. Additionally, it has a rated Iq (quiescent/no-load current) of only 20 microamps. The buck converter’s 2.2 microhenry inductor is magnetically unshielded which may cause some increased EMI (electromagnetic interference) emissions, but I don’t have the equipment to test this.
I was looking around for the battery’s protection circuit, and found it on the flex PCB that surrounds the Li-ion cell. It uses a Xysemi XB6366A protection circuit which, like the buck converter, is a fully-integrated device; there are no external protection MOSFETs for disconnecting the cell from the rest of the circuit.
December 14, 2015 – After extensive and detailed analysis (148 MB of text files!), I’ve analyzed the battery’s voltage and output capacity, which can be viewed HERE (lots of pretty graphs; check it out!).
The data doesn’t stop there. It took almost three years to track the cell’s self-discharge, but the data is finally in. The final report is available here, but previous installments are available here (Part 1), here (Part 2), here (Part 3), here (Part 4) and here (Part 5).
Oh wow, already a week since the event finished; I need to get posts written up more often!
Anyway, the last 2 days of the event were pretty much information seminars with three separate ‘tracks’ with one of them being all about fuel gauges (you can guess which one I went to 🙂 ). They discussed the reasons that fuel gauging is so important (and why “just measure the voltage” usually isn’t good enough), and also explained why your battery life just plummets after a few hundred cycles or 20% wear.
One of the main fuel gauge guys at TI gave me an evaluation board for their latest-and-greatest fuel gauge, the bq40z50. This gauge is able to handle 1-4 cells in series, which means that you can now pack a laptop battery’s smarts into a battery meant for a smartphone or tablet.
I’d post more but these few posts were “Mini-Rambles” after all. I may post a few pictures later on.
Today was the first day of the actual Texas Instruments Battery Management Systems event. To my surprise, a couple hundred of people showed up from TI employees, a lot of customers (representatives from various companies like Bose, Google, and many others), and me as well. 🙂
The first day was a basic but still detailed introduction to the inner workings of Li-Ion technology as well as its limitations, failure modes (the gas coming from a Li-Po [lithium-ion polymer] cell contains carbon monoxide, hydrogen and a bunch of other gases), with this leading towards battery fuel gauges and why just measuring the voltage is not enough to accurately determine how full a battery is.
The day ended with a lab showcasing TI’s new Gauge Development Kit (GDK), which, in layman’s terms, is a “battery lab on a board”. It includes PC communication hardware, an adjustable charger, adjustable load and an on-board fuel gauge (but it’s set to use an external fuel gauge by default). I even got a chance to talk the TI battery management team, and even had a dinner with a few key TI guys including the one who made THE design for the GDK.
Woohoo, travel time! Today marks the first day in Dallas attending Texas Instruments’ Battery Management Systems deep-dive seminar. Okay, technically it doesn’t start until tomorrow, but that doesn’t mean today was any less exciting.
The flight from Calgary to Dallas wasn’t too eventful, besides a controller fault that required going back to the terminal to resolve, but trying to grab a SIM card to put in my phone was a whole other ordeal. Fry’s carries the card but doesn’t carry the refill PINs, and my Canadian credit card would not work both online and on the phone; it was only when I went to Best Buy to purchase a refill card with cash that I was finally able to get cellular phone and data access.
I was also given a tour of the main TI facility, and boy it is HUGE! As much as I would have loved to share images, I signed an agreement explicitly stating I cannot do so. However, I was able to see a bunch of the lab rooms, offices and demo stands showcasing various TI technologies at work, such as the ARM processors in the Nest thermostat, the DLP chips in pocket projectors, and so on. I even got to see many of the people in the TI Battery Management team in person, but because of the seminar running from Tuesday to Thursday, they were visibly too busy with work to have a chat.
Tomorrow marks the first instalment of the Battery Management Deep-Dive Training sessions. There is preliminary word that I may have an opportunity to speak in public for a couple minutes about the TI forums and why I’m here.
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.
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.
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.
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.
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.
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 ****
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.
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
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.
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.
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 email@example.com!
[EDIT – August 2, 2016] Whoops, looks like I never had the button working in the first place. Hopefully it works this time.
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) (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)|
Now that I’ve been amassing a greater and greater arsenal of iPhone batteries, it’s gotten to the point that it makes most sense to create a connector board that can bring out the Pack+/Pack- pins alongside the HDQ data pin so I can view the gauge’s status in GaugeStudio.
Why use iPhone batteries in DIY projects?
The benefit of using iPhone batteries (note they must be for the iPhone 4 or newer; older ones will lack the fuel gauge) in microcontroller-based projects, is that the fuel gauge allows the microcontroller’s program to read out its current battery level, power consumption, capacity and time-to-empty; you also get the usual built-in protection circuit to safeguard against short-circuits, overcharge/overdischarge and overcurrents.
Additionally, iPhone replacement batteries are easy to find online or in cell phone repair shops, making them cheap and plentiful.
What is this “HDQ” that I keep talking about?
HDQ is a communication bus originally made by Benchmarq (now a part of TI). It stands for “High-Speed Data Queue”, and is a serial bus that transmits data over a single wire. This, however, is not to be confused with Dallas Semiconductor’s 1-Wire protocol. The basic idea is the same but they are completely incompatible with each other.
The board was made up of an iPhone surface-mount connector, a 4-pin connector for HDQ data transfer, a 2-pin male header, and a 2-terminal screw terminal. As with many of my prototype boards, wiring of the board is done with thin, flat solar cell tabbing wire. It’s flat, pre-tinned, and can handle high currents easily.
The benefits of this sort of board is that it allows:
Although I could have created one large breakout with all the available connectors populated, I wanted to be able to use multiple batteries at once for powering different devices. Additionally, the HDQ bus has no support for addressing multiple devices.
The iPhone 4, 4S and 5 batteries have an additional NTC thermistor pin, but I have left them disconnected since I can read out the battery temperature over HDQ anyways.
Keep in mind that not all Li-Ion batteries have the same charging voltage. The iPhone 4 and 4S batteries use a 3.7 volt cell, charging at 4.2 volts; but the iPhone 5, 5S and 5C batteries are 3.8 volts, charging at 4.3 volts. 4.3 volt cells can charge at 4.2 volts with a capacity reduction of 5-10%, but 4.2 volt cells must not be hooked up to a 4.3 volt charger. There is overcharge protection built into the battery but it should not be relied upon for regular charging. Apart from the usual risk of the battery catching fire (or even just puffing up like a balloon), you also permanently decrease the battery’s capacity and dramatically increase its internal resistance, essentially crippling the battery for life.
In the wake of my previous teardowns of the iPhone 4 and 4S batteries, I went onto eBay and Amazon (realizing that they finally have Amazon Prime student rates up in Canada) and bought a few iPhone 5 and 5S batteries. Although I was primarily interested in trying to get the gas gauge information out of the batteries, I had a secondary reason. The Nexxtech Slim Power Bank (a subject of a separate blog post) uses a pair of 3.8-volt Li-ion polymer batteries, and they seemed to be be suspiciously similar in size to what is used in the iPhone 5. But enough of that, we’re here for the iPhone 5 battery in particular!
The iPhone 5 battery measures 3.7 mm in thickness, 3.2 cm in width and 9.1 cm in length. This particular model, made by Sony, has a model ID of US373291H, with the six digits corresponding to the cell’s dimensions. This cell has a labeled capacity of 1440 mAh at a nominal 3.8 volts, with a maximum charge voltage of 4.3 volts. I tried to read the data matrix barcode on the cell but my barcode scanning app on my phone refused to recognize it. I might try to scan and sharpen the barcode later but it’s not something that’s of a high priority to me.
Battery Teardown and Pinout
The board itself is rather interesting. The protection MOSFETs used to switch the battery’s power are chip-scale packages and are glued down with epoxy, same with the gas gauge itself. This means that I can’t easily replace it with a rework station if the need arises. The board includes the gas gauge, thermistors, protection circuitry and still has room for a polyfuse for extra over-current protection.
The pinout of the iPhone 5 battery is pretty much the same as of the iPhone 4 and 4S. You have Pack-, NTC Thermistor, HDQ and Pack+. In this particular model of battery, the gas gauge is a bq27545 (labeled SN27545), but has basically the same feature set as the iPhone 4/4S’ bq27541. With this information, I soldered to the small terminals on the connector (the actual connectors for this battery haven’t arrived yet since it takes so long to receive items from China on eBay), and hooked it up to my trusty Texas Instruments EV2400 box.
And once again, we’re presented with an obscure firmware revision. The latest bq27545-G1 firmware is only version 2.24, but this chip has version 3.10. After forcing GaugeStudio to accept this gauge as a -G1 version, we’re once again presented with a sealed chip. Let’s try to unseal it with the default key…
… and I get the dreaded “Unseal Key” prompt. Cue the dramatic Darth Vader “NOOOOO” here. Maybe Apple read my previous post and decided to change the default keys this time (Hey Apple, if you read this, make the iPhone 6’s gas gauge have the default keys again)! This means that not only can I not access any of the juicy details of this battery, but I cannot update its firmware to a more… conventional version either. I could try brute-forcing it, but trying to hack a key with a 32-bit address space over a 7 kbps bus… uh, no. That’s not going to happen. I’d probably have better luck reverse-engineering Apple’s battery code but I doubt they have any facility to do in-system firmware updates for the gas gauge.
Now for some rather… interesting details of what we can access. The design capacity of this battery, according to the gas gauge, is 1430 mAh, same as the iPhone 4S and also 100 mAh less than what’s written on the label. That, and the full charge capacity of this battery is 1397 mAh out of the gate. The gauge seems to be an insomniac (it won’t enter Sleep mode even when the battery is not hooked up to any load), and it seems to have less features despite having a higher firmware version (I’m sure the internal temperature isn’t 131 degrees C…), and the Pack Configuration register doesn’t bring up any sensible data.
One thing that I haven’t confirmed is whether or not this battery had been tampered with before I received it. I bought this particular battery from eBay and it was listed as new. It had some adhesive residue but no obvious sign of being peeled off from another iPhone. The cycle count is set to 1, and because the gas gauge is sealed, I can’t read any other data like the lifetime data logs. There is a chance that this battery isn’t new and that the seller had somehow changed the data memory and sealed the chip with a non-default key, but I need to wait until some other batteries arrive in the mail and perhaps try reading out batteries taken out directly from some iPhone 5s. Until then, it’s only speculation as to why this chip is sealed with a different key.
victims specimens: an iPhone 5S battery, a “new” iPhone 4 battery, and an Amazon Kindle battery.
(UPDATE: March 2, 2015 – I’ve picked up a pair of the newer tamper-resistant versions of this wall outlet.
A review and teardown on that unit is coming up; stay tuned!)
(UPDATE 2: May 29, 2016 – Scratch that on the first tamper-resistant model; it had the same performance as the one mentioned here. Also, Costco has released a 3.1A version of this outlet, and is currently under review.)
About a week ago I bought a set of wall outlets from Costco that integrate two USB charging ports into a standard Decora-type receptacle. It’s marketed to replace your traditional AC adapter, allowing other appliances to be plugged in while charging your portable electronics.
The outlet is made by Omee Electrical Company, but curiously enough this particular model, the OM-USBII, wasn’t listed on their site. The packaging itself bears the name Charging Essentials, with a logo that looks like a USB icon that’s had one Viagra too many. The packaging states that the outlet has:
The second note is of particular importance to me. If it’s true, that means it might be using some USB charge port controller like TI’s TPS251x-series chips. But I’m not one to have blind faith in what’s written on the packaging. Let’s rip this sucker apart!
The outlet has a snap-on coverplate which may look sleek but could hamper removal of this outlet later on if needed. I was curious as to why one couldn’t just use a regular screw-on coverplate, and it turns out it’s because the mounting flange doesn’t have any tapped screw holes; you physically can’t use screws on this because the manufacturer didn’t want to go to the effort to make holes that can accept screws!
The casing is held together with four triangle-head screws in a weak attempt to prevent opening of the device. I had a security bit set on hand so this posed no hindrance to me. Upon removing the cover, the outlet seems rather well built. However, after removing the main outlet portion to reveal the AC-DC adapter inside, I quickly rescinded that thought.
The converter seems relatively well-built (at least relative to some crap Chinese power supplies out there). Some thought was put into the safe operation of this device, but there’s almost no isolation between the high and low voltage sides, and the DC side of this adapter is not grounded; the “ground” for the USB ports floats at 60 volts AC with respect to the mains earth pin. The Samxon brand caps are also pretty disappointing.
As for the USB portion of this device, I had to remove some hot glue holding the panel in place. After a few minutes of picking away at the rubbery blob, I was able to pull out the USB ports.
… and I found LIES! DIRTY LIES! There is no USB charge port controller, contrary to what the packaging claims. It just uses a set of voltage dividers to emulate the Apple charger standard, which could break compatibility with some smartphones. Ugh, well let’s put it back together and take a look at it from the performance side of things. At least the USB ports feel pretty solid…
To measure the voltage-current characteristic of the outlet, I rebuilt my bq27510-G3 Li-Ion gas gauge board so it had better handling of high current without affecting my current and voltage measurements. The reason I used this is because the gauge combines a voltmeter and ammeter in one chip, and by using the GaugeStudio software, I could create easy, breezy, beautiful V-I graphs.
Using a Re:load 2 constant-current load, I slowly ramped up the load current while logging the voltage and current data to a CSV file for analysis in Excel.
This charger’s… okay. It has surprisingly good regulation up to 2.3 amps, but after that point the AC-DC converter basically brickwalls and the voltage plummets to 3 volts. That said, this also means that this outlet is not a set of “two 2.1A USB ports”. You can charge one tablet but you won’t be able to charge a tablet along with another device simultaneously.
Bah, I’ve had it with this wall outlet. Looks like this one’s gonna be returned to Costco in the next few days. This outlet may be adequate for some people, but for me it’s a disappointment.