I was recently doing some research and came across a couple interesting pages about batteries.
The second article I found was a very interesting page about building your own battery packs and chargers. The author of the article was able to cut his charging time for his cordless power tools in half with his smarter charger.
http://www.angelfire.com/electronic/hayles/charge1.html
I recently started having a lot of problems with my aging cordless drills, so I may start a project for this.