I feel I should be thanking you, Sam. Knowledgeable volunteers like yourself on websites like this make life easier for a lot of people. Sorry for reviving an old thread, but I felt the need to add my personal experience. You are correct that, even though it's unlikely that multiple batteries would fail at the same time, I too might have replaced my batteries first and then had to spend additional money on a new charger. Luckily I had a second charger to check my batteries. My chargers are identical, except that one was killed by using it with an inverter and the other still works. FYI both of my chargers are Craftsman #1425301, one hour chargers, rated for 7.2 to 24 volt batteries. (Although I've read that this model doesn't work with some Craftsman 16.8V batteries.) My 4 batteries are NiCad, 19.2 volt "EX" type. I came across this thread looking to repair my dead charger. It appears that it only needs an inexpensive comparator IC to fix it. I guess I'll find out once I have the part soldered in.