Interior dome lights and headlights dimming and batteries do not fully charge

2013 CHEVROLET SILVERADO
42,841 MILES • 5.3L • V6 • 2WD • AUTOMATIC
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BEARANGEL
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I am having a problem with my interior dome light and headlights dimming, both when idling and driving. Batteries not fully charging also.

I have been to a mechanic and they checked the alternator and both batteries (had an extra battery installed under the hood due to having a truck camper that I live in in the bed of the truck. (See attachment) This mechanic was the one that said batteries were not fully charging.

The alternator is good, but the the batteries are not charging fully. Is the extra battery causing the problem? Do I need to install a stronger alternator or take out the extra battery?

Help please.
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Jan 21, 2017 at 9:44 PM
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STEVE W.
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Are both batteries good? Have them both load tested.
How do you have them connected, Battery isolator or just parallel cables?
Are both batteries the same type and size? If you are not using an isolator for the camper battery they need to be or the system will stop charging as soon as one battery shows full charge.
If you disconnect the extra battery does the original battery charge up?
Jan 22, 2017 at 4:15 AM
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BEARANGEL
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Both batteries are the same size and were load tested. Both are good.The guy that put them in, last year, did parallel cables and a special fuse (don't remember what he called it) to keep them from overcharging.

I did not think of disconnecting extra battery, so don't know. Will have some time off from work on Wednesday to try it and will let your know then. Thank you for the help.
Jan 23, 2017 at 2:30 PM
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STEVE W.
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OK if the batteries are good the issue almost has to be something like a bad cable or connection not allowing them to get full voltage. Or the second battery wasn't wired in correctly. The alternator itself is a high output unit that should easily charge both batteries.

There is a good write up on the method here:
http://www.silveradosierra.com/how-to-articles/how-to-hook-up-dual-batteries-factory-style-t284010.html
Basically follows the factory book but with better pictures.
Jan 23, 2017 at 5:23 PM