Hi, I have searched the forum for the answer to my question, but haven't found the exact answers yet. I think I may have two problems but wanted to run it by you guys just to make sure. Last winter I had a battery go bad, so I replaced both batteries with 850cca batteries. I was driving the other day and noticed the battery indicator was lit on my dashboard. I looked at the volt meter and it was low. I stopped to go into the store and when I restarted it was fine, but that was short lived. I checked all of the plugs and they all seem fine. I checked the voltage at the battery while the truck was running and am getting only 12.08 volts (which in my opinion indicates a bad alternator). I turned the truck off and checked the voltage on the batteries and I am getting 12.18 vdc on the passenger side battery and only 10.7 vdc on the drivers side battery. Is it safe to assume that my alternator is bad and also a battery, or is it that the alternator is bad and the battery on the drivers side is just pulling more? Thanks for any and all help.

 

Personally what I would do is to disconnect both batteries and charge them with a trickle charger. While doing that i would take the alternator off and have it tested at an auto parts store. You could just drive the truck to the store if you want to. I would also have the batteries load tested after they get charged. It's hard to tell what actual battery voltage is when the two are connected to one another. It does sound like your alternator is bad. You should have about 14.4 volts with your truck running. I would also check all your connections for your battery and charging system. Hope this helps.

Red

 

Check your positive cable connecting the two batteries too. Possibly a bad alternator and that cable I mentioned.