Last fall my batteries were getting weak. I assume they were the OE. I bought the Ex with 62K on it. I searched the forums and found pretty good reports on Autozone Duralast Gold batteries, so I purchased two and was amazed at the way they spun that thing up at the touch of the key. However the last couple of months they seem to be getting tired to where at times I'm not sure its going to start. I believe my alternator is failing and have ordered a new one. To insure that its not the batteries I went back to AZ and asked for a test. A nice lady who may or may not know that much about batteries obliged and rolled an impressive machine out to the truck and hooked it up to one of the batteries for a test. I asked her if we should unhook one of the batts for the test and she said no she could test them hooked up. It seems to me since the batteries are wired parallel that it would be necessary to isolate them in order to see if one was weak. Can anyone clarify this procedure for me? Thanks

Ben

p.s. She said they were both good.

 

They need to be isolated from one another when testing or you will get the reading from the strongest battery. You can still leave one hooked up to the vehicle though.

 

You're doing the right thing by beginning to troubleshoot for the problem. It's not very likely that both sets of batteries went bad on their own. The first thing I would do is clean the battery terminals and check for loose or corroded cable connections between battery and alternator and starter motor. Might not be an issue but it's free... and free is a good thing. Check for loose connections while the battery cables are disconnected. Don't want any nasty surprises when sparks fly.

I think your first guess is good that the alternator output isn't sufficient. Have a reputable shop check for proper charging voltage and current, unless you can do it yourself. If your batteries are down on charge as much as I suspect then it could take hours to charge up again. Batteries low on charge will pull down system voltage and a not so saavy mechanic might think your alternator doesn't charge to specification and want to replace it. Take that noise out of the equation by charging your batteries overnight the day before you drop the truck off for service. It will help the mechanic to pinpoint the problem as to why the batteries are discharging.

If that doesn't pan out then you might have a high resistance short in the electrical system that is discharging the batteries when the truck is parked. Light bulbs are common culprits but it could be about anything from burned electrical devices to a harness rub on chassis.

Get this fixed soon. Cranking batteries don't like to sit at reduced state of charge and the life can be sucked out of them. Get the charging system working right so you can properly maintain your batteries and not have to buy another set.

 

For the record, a fully charged automotive lead-acid battery will sit above 12.6 volts. Using a digital volt meter, check each battery with them disconnected from the vehicle.

If they are below that, use a battery charger at 10 amps or so, and let them sit for an hour on the charger. Disconnect the charger, reconnect to the vehicle, turn on the headlights for a few seconds (to remove the "surface charge"), turn them off, and then check the voltage again. After a few times of doing that (how many times depends on how low the batteries were to begin with), if they do not recover back to 12.6 volts or higher, they are going bad. How bad the batteries are depends on how low the voltage is. 12.5-12.4, they are "mediocre". Anything less than 12.3 is less than 50% charge, so they are toast.

For a diesel, I wouldn't put up with anything that would not charge to a full 100% (12.6 volts).

 

Thanks for the input guys. I have checked the connections on everything except the engine to frame ground. Can't find it. ?? The voltage on each battery with no load was in the 12.4-12.5 range. I have them on a sophisticated trickle charger now and it took about 3 days to get them up to float charge level. They now check at 12.7 with no load. The alternator is putting out a max of 13.9 volts with nothing on. It drops to the 12V range with the AC on, which is always here in Florida.

Ben

 

It should be above 14, and not drop that far with the AC on.

Check all the connections between the alt and the batts. And the grounds. There is one ground from the firewall to the frame I think, but there are others.