That's a cool idea... I never thought about that before. I bet a couple Dewalt packs would do it. Heck.. this would be great for a race car/motorcycle, etc where the weight of a lead acid is bad...
I charge my 4s A123 pack straight off my vehicle's "12v" system... about 14.5v.
20 cells.... good for a 5p pack... I can't see how that wouldn't do a good job. Hmmm
But there is also those killer Optima batteries that would be much easier... and cheaper :)
http://www.1st-optima-batteries.com They are awesome... but I have never plunked down the $150-200 to get one myself.
Brian... I can get new batteries (either ACDelco or Factory house brand) for $25-30 if you are interested I'll tell you how/where here in town.