ltc, that is a good suggestion but what if the flight battery fails?

Personally, I'd like to see a system that would consist of a high voltage BEC, say 5 A / 6 V (or adjustable from 5.5 V to 8 V), a connector for 2S backup battery and a charger circuit that would keep the 2S battery charged. Additionally there should be at least a power switch and a load switch with logic that would switch over to the backup immediately if the BEC output goes out of limits. Optionally over voltage protection and some monitoring functions could be included.

The idea behind this is to avoid dual RX batteries that you need to remember to charge every time and save weight too. I have heard the heli guys have something like this but so far I have not found one optimized for F3A use. If I don't find anything, I might just design this myself... Rune, I think we will meet at the Nordic F3A championships in a few weeks. We could discuss this there and find out if others have same kind of needs.