I have by no means whatsoever read this entire thread so I am wondering if anyone has tried using 12v (or even 13.6v) battery packs from power drills? Seems like I could pick up some on ebay for cheap. Could even run a few in parallel

Or how about a battery from a small UPS. Those are cheap on ebay as well. Only problem is weight



Question also:
What has proven to be the best option for smart charger for SLA batteries