Pickup with 2 batteries--one battery continually loses charge

The battery that loses charge has been checked and said to be in good shape. I’m planning to get it rechecked. The other battery holds charge very well. The batteries are hooked up in parallel. If one battery holds charge and the other doesn’t, shouldn’t that limit the places to look for a short in an electrical line or device?

One battery is losing its charge to the other.

You need a battery isolator like this one:


(Hope that link works, if not, just go to JCWhitney.com and search for “isolator”.

What kind of truck? If they are hooked up parallel to each other, then there could be a problem with the cable connections on both batteries. I’d clean the terminals, and consider replacing them if caked with corrosion. Corrosion on either battery will prevent the batteries from charging and discharging evenly, as this set-up is most likely designed to do.

Did you check the other battery? If the other one’s bad it can drain the good battery.

The easy way to check if it’s a problem with the batteries themselves or something on your rig would be to switch the batteries and see if the problem moves with the battery or not.

It’s a 95 Chevy Silverado 3/4 ton 4 x 4. There is no corrosion–recently cleaned… Thanks.

Good idea on switching places with the batteries. I’ll try it. thanks.

This is the 3rd time I’ve tried a response–the first two didn’t show up. Anyway, I’ll have the system checked. If there is an isolator I suppose it could be defective also? thanks

Okay, if it’s a newer factory setup, isolation is probably either controlled through a solenoid or a diode pack (which is essentially what an isolator is). Either way, the JCWhitney link that I posted isn’t going to help much. BUT, hopefully it won’t be an expensive fix with parts designed for the factory system. GreasyJack’s idea of switching the batteries is a good one.