Battery Charger/Maintainer Does Not Seem To Work Correctly

99novice

I have a 3 amp DieHard Battery Charger/Maintainer that I’ve hardly used. I recently connected it to 3 batteries: 1) an old battery, 2) and older battery that still seemed to work well in my car, and 3) a new battery that I installed yesterday (that works perfectly in my car). When I’ve connect the Charger/Maintainer to the 3 batteries, I get the same reading – It initially shows “CHARGING 6v 2%” and after about 45 minutes says “CHARGING 6 v 5%.” I’ve disconnected the Charger/Maintainer because I don’t want the seemingly very good batteries recharged to 6 volts instead of 12 volts. Is this a defect in the Charger/Maintainer or do all similar charging devices initially show them charging at only 6 volts? (Also, my new battery shouldn’t need ANY charge – I only connected it to the Charger/Maintainer to see what it said. I assumed it would have charged for a few minutes at 12 volts and then turned off due to it being fully charged). The instructions say nothing about this issue and Sears customer support says the batteries must be dead (and I know all 3 work perfectly and start up my car every time). In addition, the older battery was tested by a much larger and more sophisticated machine by my mechanic and was shown to be in perfect working order. I’m guessing the microprocessor or computer in the Charger/Maintainer is defective. Any thoughts or advice is appreciated