On Wed, 26 Feb 2014 14:33:33 -0600, Jon Elson
wrote:

Tom Gardner wrote:

Thanks for all the replies and knowledge. My other battery charger is a
one pound electronic machine. It works OK, supplies 2, 6 and 12 amps
and has all sorts of buttons and lights! What it won't do is charge a
totally dead battery...thus repairing the old Craftsman. It displays:
"BAD BATTERY" and I have to hook-up jumper cables from another vehicle
to get a few percent of a charge to get the electronic charger to work.
I went through this when stranded at a remote cabin with a car with
a dead battery. Most of these smart chargers have some stupid
secret code to "rejuvenate" a totally dead battery. You may have
to push multiple buttons, hold for several seconds or whatever, and
no way to figure it out without the manual. I had to play with that
unit for MANY minutes before I was able to translate the Chinglish
instructions into the right buttons to make it start charging.

Jon
The reason they won't charge a dead battery is the "polarity
protection" circuit to prevent hooking the charger up backwards and
doing damage to either the charger, the battery, or both.