@felmue I think 4.35v are somehow coming from the charging cable, because as soon as I connect the charging cable the M5.getBatteryVoltage() / 1000.0 giving me 4.35v but if I remove the charging cable then I get the actual battery voltages e.g 3.8v.
Is it possible that somehow I can read the actual battery voltages even if the device is connected to the charging cable?