I own DOZENS of cars and teeruks. When I run the batterys down to the ground, and electronic microprocessor controlled charger, which may be 100% of what's on the market, will NOT charge my dead battery, as they need even the tiniest signal to make sure they're not improperly connected etc. So I buy so called "buzz box" old skool battery chargers at swap meets. Their too dumb to know if mis connected etc. I have a dozen for so my 50 or so vehicles