Get battery charge levels from firmware.
Return value: uint8_t battery status
0x01 battery_full (if battery percentage is >= 80)
0x02 battery_med_high (if battery percentage is >= 60 and <80)
0x03 battery_med_full (if battery percentage is >= 40 and <60)
0x04 battery_med_low (if battery percentage is >= 20 and <40)
0x05 battery_low (if battery percentage is <20)