1990 V6 camry runs well then battery is fried. Is this related to overheating or electrical problem?

Question

I have replaced the alternator (2nd one in 2 years). Power fades when driving. New alternator performed well, then the car died. Battery was reading 5 volts, but alternator was working well. Replaced the battery with a brand new one. They checked it and it is working properly. Alternator is charging correctly. Drove 1000 km fast driving. Seemed to be running very well but overheating. The cooling fan did not come on when stopped. Could hear fluid bubbling when checked engine. Now the car died again. Alternator was checked at dealer as ok, but new battery is reading 5 volts and cannot be charged. Will need to replace it. Dealer says the problem is only the battery. Is there something else which is causing the battery to become fried if the alternator is working correctly? How could this happen? Been living with this for about a year, and I am ready to give in. Assistance is appreciated.

when the new battery was installed, they tested the alternator on the car, and it was working in the correct range. I took two long trips prior to both times battery becoming unusable. The newest battery was run down, and when I was stranded, the tow truck driver said it was reading 5 volts. It was towed to dealer, they may have tried charging it briefly but I doubt it. It reads 9.2 volts this morning, and I am charging it at 2 amps trickle charge. If it gets up to 12.5 volts, then I will put it back in the car. Other points. I have been using a small power inverter to run a cell phone charger in the car. The air doesn't work, so I don't use that. There is a display error which says Lights that is always on when car is running, but no other lights. The timing has not been changed in 2 years. There was a loose connection to the positive terminal, so I replaced it with a battery cable that is longer and fits much tighter on the battery terminal. Maybe this cable is not ideal

Answer 1

Was the alt. tested on the car or off. The alt. testing good on the bench means nothing. The alt. must be checked at the battery posts. With alt. installed and engine idling you should get approx 15 volts across battery terminals. The meter on your dash should show charge also. A battery is not fried just because it reads 5 volts. This only indicates it was discharged. It should charge up normally if alt. is working correctly. It follows your alt. is not putting out or the batt. wouldn't be discharged. The engine fan can't run on 5 volts so it is probably ok. I suspect you have a broken wire between alt. and battery or a blown alt. fuse.