Regmax is a DualBat input booster 1S2P Lipo or LiFe, 3 or 4 Nimh input, 5V5 4A output. Booster means that it is able to elevate the voltage from 3.7 V to 5.5V with a efficiency about 85 % which is pretty good.
I will install it in my Wasabi. The total weight of 2 LiFe 1S batteries + the regmax is lighter than a 4 cells R6 battery, but provide a higher capacity.
The redundancy is total. There is no primary and secondary battery. As soon as you unplug a battery the device switches automatically to the second battery. When the 2 batteries are connected and running fine, a green led is ON.
A video is better than 1000 words, so here it is:
Greentronic is not only manufacturing this Regmax, but also different other voltage regulators or dual power.