Each iPhone generation since the iPhone 4 uses a TI gas gauge and uses the HDQ bus 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).
If anyone has any iPhone 5S, 5C or 6 batteries that they’d like to donate, give me a shout! :)
|Model||Gas Gauge||Firmware [note 1]||Designed Capacity||Default Unseal Key||Comments|
|iPhone 4||bq27541||1.25||1420 mAh||Yes (0x36720414)||Likely the easiest gas gauge to get a hold of.|
|iPhone 4S||bq27541||1.35||1430 mAh||Yes (0x36720414)||Similar to the iPhone 4 but with a different firmware version that seems to function identically.|
|iPhone 5||bq27545||3.10||1430 mAh||No (not yet known)||No unseal key found yet. Will probably need to brute-force the key somehow…|
|iPhone 5S||?||?||?||?||Have not yet acquired a battery of this type|
|iPhone 5C||bq27545||3.10||1550 mAh [note 2]||No (the model I purchased has a different unseal key but I was able to retrieve it. I am not sure if it is consistent with other packs yet.)||Need more samples to confirm. Not publicly disclosing this key as the “Big A” might be reading this…|
|iPhone 6||?||?||?||?||Someone get me one of these, please. :)|
- 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.
- 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.