i.m.o. cordless drill is the way to go here. buy a cheap used flashlight for whatever brand of battery you use around the shop, chop off the flashlight portion and just use the plastic termal/disconnect part at the bottom.
i did some math using the 5.0 AH m18 milwaukee shit i use at home, it would run LED head and tail lights for a really long time.
i did a bunch of research into this a couple years ago and in the end nothing made as much sense for a total loss system.