12 Volt Lithium Battery Individual Cell Regulator

should be able to parallel them

this designed to mount 'on' (3) 18650 cells
and those strap conductors are spot welded .. NOT soldered to the batteries

the DIY crowd are building their own spot welders using motorcycle size batteries
i watched some vids on youtube

the cells could end up being expensive if you buy new
if you buy used, you need a tester to find and grade the good ones from the bad ones
when building packs, you want them to have matching test/grade settings