Batshare
The Smart-Fly BatShare enables you to use two battery packs and two switches to provide Dual-Redundant security to your airborne system, just like in full-size aircraft. With the Smart-Fly BatShare, you can tolerate a single failure (open-circuit, short-circuit, low voltage) in either battery pack, or switch, or battery wiring, without losing radio control.
The Smart-Fly BatShare continually monitors both battery packs and switches for the one with the higher voltage, and routes that to your Rx and servos. You may combine different size packs. In practice, with two good packs, the BatShare draws power equally from both packs, adding their individual capacities. I.e., if Battery #1 is a 6V/1350mAH pack, and Battery #2 is a 6V/2700mAH pack, you will have 4050mAH power supply onboard, with at least 1350mAH to fly on, in case of a failure.
The Batshare can be used with battery packs with a minimum voltage of 5.5V up to a maximum voltage of 30V. 4.8V NiCd/NiMH will NOT work with the BatShare.