I came across a huge web site called Wheelchairdriver.com

It's run by a disabled Englishman who has done extensive work on building and modifying electric wheelchairs for his own use, and who has researched a lot of the associated technology, such as batteries, chargers, and control systems.

He has a very good and detailed page on a high-tech ultra-flexible battery charger here:

http://www.wheelchairdriver.com/hyperion.htm

From there you can link to all his other pages, such as discussions of the different types of batteries, including lithium, also motors, control systems, etc. His info is current and very application-oriented.

You might also want to check out his pages on how he built an off-road electric wheelchair - some good ideas there.

All in all, an interesting resource if you're planning to add an electric component to your build.