Eww, those wall chargers are crap. They either rely on the output resistance of the tiny transformer inside to limit the charge current, or charge through a resistor. In either case, there is no charge limit whatsoever. I suppose it's ok if the charge current is really really small, but not the best IMO.
To charge the batteries in all my household items (remotes, cameras, etc), I took a radio
shack charger, gutted it, and added terminals to hook to my "real" chargers. What's nice about this is I can charge 1 to 4 AA's or AAA's, or a 9v battery in one package.