Seeed Xiao nrf5240 - battery voltage reported 0.9V below the actual voltage

[RobsonMi]

I did test this on 2 XIAO's from different sources. On both charging stopped at 4.11V indicated in MC app but the cell was actually 4.2V as it should. I suspect there is a slight offset in the programmed ADC multiplier. Can I correct this myself somehow?

[446564]

The firmware probably just needs fixing, you can see the function that gets the voltage here

MeshCore/variants/xiao_nrf52/XiaoNrf52Board.cpp

Lines 66 to 72 in 10067ad

	uint16_t XiaoNrf52Board::getBattMilliVolts() {
	// https://wiki.seeedstudio.com/XIAO_BLE#q3-what-are-the-considerations-when-using-xiao-nrf52840-sense-for-battery-charging
	// VBAT_ENABLE must be LOW to read battery voltage
	digitalWrite(VBAT_ENABLE, LOW);
	int adcvalue = analogRead(PIN_VBAT);
	return (adcvalue * ADC_MULTIPLIER * AREF_VOLTAGE) / 4.096;
	}

And the defines being referenced here

MeshCore/variants/xiao_nrf52/variant.h

Lines 75 to 76 in 10067ad

	#define AREF_VOLTAGE (3.0)
	#define ADC_MULTIPLIER (3.0F) // 1M, 512k divider bridge

I think the multiplier needs adjusting add I've seen similar issue with my xiao.