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)