Low voltage isn't the problem I'm having. Although it is always a factor to watch. I can't remember ever going below 10 v on my 3s's. However, my big problem is almost always the "sandwiched" cell getting too hot (as near as I can figure). Which in turn is killing the lipo. I am currently using 20C 2100-2150's which should easily handle the Rex's amp draw (currently 28 amps according to the meter) and is no where close to the Blade (12 amps). When I recharge, the packs have usually been sitting for at least an hour. Yet I have to still be somehow overheating the pack. I have had three middle cells go bad now. The two outside cells are fine. But since these 3s's are from different manufacturers I can't recombine the packs to make new ones. So now I have three 2s's which are only good for my smaller planks. And before you jump to conclusions, I'm charging at .5 amps. I have thought about inserting a spacer between the cells to allow for cooling, but real estate is limited on the HDE as far as battery space and even tighter on the blade.