docs: def battery_discharge_current(self):
          """ Returns current in mA """
          msb = self.bus.read_byte_data(AXP209_ADDRESS, BATTERY_DISCHARGE_CURRENT_MSB_REG)
          lsb = self.bus.read_byte_data(AXP209_ADDRESS, BATTERY_DISCHARGE_CURRENT_LSB_REG)
          # 13bits
          discharge_bin = msb << 5 | lsb & 0x1f
          # 0 mV -> 000h,	0.5 mA/bit	1FFFh -> 1800 mA
          return discharge_bin * 0.5