docs: def internal_temperature(self):
          """ Returns temperature in celsius C """
          temp_msb = self.bus.read_byte_data(AXP209_ADDRESS, INTERNAL_TEMPERATURE_MSB_REG)
          temp_lsb = self.bus.read_byte_data(AXP209_ADDRESS, INTERNAL_TEMPERATURE_LSB_REG)
          # MSB is 8 bits, LSB is lower 4 bits
          temp = temp_msb << 4 | temp_lsb & 0x0f
          # -144.7c -> 000h,	0.1c/bit	FFFh -> 264.8c
          return temp*0.1-144.7