I can keep it short because Jeff Atwood gives you a decade's worth of experience with rechargeable batteries in a post of a mere thousand words or so, called Adventuries in Rechargeable Batteries.
Bottom line: fast-charge battery chargers can ruin rechargeable batteries.
Atwood tells you to spend a little more -- forty bucks on a battery charger -- and take advantage of the fact that modern batteries, if handled carefully, can handle hundreds of charges.
Plus, this charger can charge not just the usual "A" and "AA" batteries, but also the much bigger "C" and "D" batteries. And you can see the charge flowing into the battery, and track its progress.
While I'm employed, will try this, and report results in a month or so.