Add a battery level reward

def reward_battery(self):
        """
        Add a battery level reward
        """
        if not 'battery' in self.mode:
            return
        mode = self.mode['battery']
        if mode and mode and self.__test_cond(mode):
            self.logger.debug('Battery out')
            self.player.stats['reward'] += mode['reward']

            self.player.game_over = self.player.game_over or mode['terminal']