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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def battery_voltage(self):
 """ Returns voltage in mV """

        msb = self.bus.read_byte_data(AXP209_ADDRESS, BATTERY_VOLTAGE_MSB_REG)
        lsb = self.bus.read_byte_data(AXP209_ADDRESS, BATTERY_VOLTAGE_LSB_REG)
        voltage_bin = msb << 4 | lsb & 0x0f
        return voltage_bin * 1.1