If you buy RC Lithium batteries, make certain they have a protection circuit/module/PCB/PCM installed that covers short-circuit, over charge, over discharge, and includes a current limiting resettable fuse. Some, especially airplane and helicopter batteries, do not. "ROAR approved" batteries for RC car racing must have these things.
If I were you, I would only use LiFePO4 chemistry, AKA "LFP" or "Lithium Iron Phosphate," batteries. Compared to regular lithium batteries they are an order of magnitude less likely to experience "thermal runaway" and cause a fire that could burn down my home or get tapers permanently banned from my favorite venue.
An important thing to remember is that LiFePO4 batteries also have about 4X longer cycle and calendar life than regular lithium batteries or NiMH batteries. When you calculate the cost over the lifetime of the battery, this makes them the cheapest batteries you can buy, cheaper than lead-acid or NiMH! The calendar life also means they have higher energy density than regular lithium batteries after just one year past manufacture.
Be smart, use the cheapest, highest density, longest lasting, and SAFEST batteries available right now which are LiFePO4