M5.Power.getBatteryCurrent() always returns 0 on cores3 lite

[ngolf]

M5.Power.getBatteryCurrent() seems to always return 0, despite battery discharging (or charging afterwards).

Same with CoreS3 library.

This is on a cores3 lite.

[ainyan03]

Thanks for the report, and sorry for the slow reply.

getBatteryCurrent() returning 0 on a CoreS3 is expected with the current code, and #292 on develop now documents why.

The battery current is read from the hardware that measures it. That is an AXP192 on the boards that carry one, or a dedicated current sense IC where the board provides one — an INA3221 on Core2 v1.1, an INA226 on M5Tab5. On a board with neither of these, Power_Class::getBatteryCurrent() has no source to read from and returns 0. The AXP2101 on the CoreS3 provides the voltages, the die temperature and the battery percentage, so getBatteryVoltage(), getBatteryLevel(), isCharging() and getChargeStatus() all work there — the current is the one value it does not cover.

To confirm this rather than assume it, the full register space of the AXP2101 was dumped on a CoreS3 with a battery attached, once while charging and once while running from the battery, and the two were compared. Everything that responds to the charge state is a voltage, a status bit or the fuel gauge percentage:

register	charging	on battery
0x00	38	18	VBUS good bit
0x01	32	55	charge state bits
0x35	C4	5C	VBAT, 4036 mV → 3932 mV
0x38 0x39	13 A0	3F F4	VBUS
0x3A 0x3B	10 96	0F 5A	VSYS, 4246 mV → 3930 mV
0x49	A3	63	IRQ / PEK status
0xA4	0D	0E	battery percentage, 13 % → 14 %
0xA9	20	21	fuel gauge status

What changed in #292 is the reporting. AXP2101_Class had a number of getters that returned 0 without reading anything, which is indistinguishable from a valid measurement of zero — exactly the situation you ran into. Those now return NaN, so std::isnan() tells you the reading is unavailable rather than actually zero. Power_Class::getBatteryCurrent() returns int32_t and cannot carry NaN, so it still returns 0, but the header now documents where the value comes from and which boards can supply it.

If you need the battery current on a CoreS3, an external current sense module on the I2C bus is the way to get it.

For what it is worth, getBatteryLevel() and isCharging() are usually enough for the common cases — showing a battery gauge, or deciding when to warn the user. If you can share what you are using the current for, we may be able to suggest something that works on this board.