readBatteryGauge

Read the device's full battery gauge (voltage, current, health, state-of-charge) from the battery service's energy / health / level-status characteristics (see BatteryGauge). Returns null when the energy characteristic is absent (firmware without the fuel gauge exposes no voltage or current) or reads back too short to decode. Absent status/health leave those optional fields null; a GATT failure reading a characteristic that IS present propagates as BrainAccessError.