comments:
I would go lithium ion and if you're planning on getting more than one, you should build it yourself. It will be cheaper, you'll get better cells and you'll always have the skills and tools if you need another one. It's fairly easy and the tools aren't expensive. Watch some YouTube videos and read r/18650masterrace. There is an Auline 4000mah 6s on Get FPV for $80. You could build a pack with nicer cells (Mollicell p42a) that would have a bit more capacity and would cost like $60 ($45 for cells, $5 for xt60/balance lead/nickel strip) and a few extra bucks for shipping). I would get this kind of spot welder for FPV packs. If you end up getting into it and building bigger packs like an ebike battery, it will be slow to recharge between welds and drive you nuts, but for a 6s pack it will be fine. https://a.co/d/0bOyFxNK (I've built 2 ebike batteries with this welder, it was slow as molasses but it did work).