I have the same switch Pablo has. It is a PowerBox Sensor.

[link=http://www.powerbox-systems.com/e/powerbox_systeme/powerbox_sensor/start.php]http://www.powerbox-systems.com/e/powerbox_systeme/powerbox_sensor/start.php[/link]

It acts as a redundant setup diverting power to both outputs in case one battery goes out. Otherwise it acts as 2 independent regulator switch systems. I use mine with one output to power the Rx the other to power my CDI. If the RX battery is unplugged the CDI battery will power both the CDI and the Rx with no interruption. The batteries drain independently so you could keep a back up fully charged.

I also have an EMS Ultimate Battery Backer. It does not work well with my Spektrum radio system. When I unplug the main battery there is a momentary lag until the Rx powers up with the back up battery. This probably would be okay in an emergency but I decided to go with the PowerBox instead.

Keven