I have a new
Black & Decker battery charger. This charger is almost too smart. It appears that if the battery is too low, my new battery charger will not even attempt to charge it (throws an error code).
When that happens, I hook my old 10amp charger to the battery; charge it for a few hours then hook up the "smart" battery charger and finish it off.
If you get a new charger, don't get rid of your old one.