Battery checker module When the battery voltage goes below the BAT_LOW level, this will toggle a GPIO/LED. If the battery voltage is lower than BAT_CRITICAL level, the LED/GPIO stays ON. The output signal can be connected to an actaul LED or a buzzer to indicated the end of battery to the user. When a LED is used, define the LED number in your airframe with BAT_CHECKER_LED. When a GPIO is used, define the GPIO port and pin in your airframe with BAT_CHECKER_GPIO. You should at least use one of these two options.