not knowing anything about brushless motor batteries
are 18650 batteries any good for brushless motors ?
are they the same as lipo's ?
There is (or used to be) more choice in chemistry in 18650 than for familiar RC stick packs. Hence the 3.6/3.7 figures you see.
Note the
C rating is much lower in cylinder cells than stick packs but it is still far ahead of NiMH & NiCd types. The C rating where I think Subculture's
folly term is spot on. NiMH advocates should think twice and compare 6 or 7 cell NiMH packs against equivalent 2S Lipo packs with a 6volt cutout. I've seen it many times, demonstrated to non competitive fast electric users that they may as well decommission their NIMH batteries if they don't use specialised chargers and do the performance checks on, so called, high discharge NiMH packs.
21700 is another popular size and it beats me why diy battery builders prefer to make 40% more spot welds in 18650 ebike packs as if there aren't enough other drawbacks. The present (@ 21/May/2021) shortage means
this wholesaler is out of stock on Samsung 18650.
Poundland powerbanks will get you cheap 2 Ah cells for £2 with USB charging. Power tool packs will give you 5s and bms. There's the mention of your choice if you were to make 18650 Lipo packs:
balance lead or BMS.