update battery level

def battery_update(self, SYS_STATUS):
        '''update battery level'''
        # main flight battery
        self.battery_level = SYS_STATUS.battery_remaining
        self.voltage_level = SYS_STATUS.voltage_battery
        self.current_battery = SYS_STATUS.current_battery
        if self.settings.numcells != 0:
            self.per_cell = (self.voltage_level*0.001) / self.settings.numcells