I used a cheap Skill for years, then moved to a Dewalt 12v, but wasn't satisfied with battery life. I'm now using a small B&D lithium from Walmart. It's small, but plenty powerful and keeps a charge for quite a bit of case prep.
Here's a link:
http://www.walmart.com/ip/Black-and-Decker-Lithium-Ion-Cordless-Drill/14971641
