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

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)

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.
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An Easy Hook-Up: Creating breakout Power/HDQ breakout boards for iPhone smart batteries

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.

Board construction

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:

  • Easy, removable connections to the battery; no need to solder to the battery terminals directly
  • Access to the HDQ data pins and power terminals
  • Real-time monitoring of battery State-of-Charge (%), current (mA), voltage (mV), capacity (mAh) and also the remaining time-to-empty (minutes).
  • Adaptability for different connectors (either by making a separate board for that connector or by creating a single “universal” board)
  • HDQ protocol can be used by a microcontroller via either bit-banging the protocol, or using an on-chip UART. (subject to a separate post in the future)

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.

Safety

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.