Old and new battery mix?

[Robojeeper53]

I have dual batteries on my truck, 2nd battery only charges when running. Now I wired the that older battery to FWC with a solid state isolator. Question will the older battery interfere with charging the new 2-AGM batteries in camper? Isolator goes on/closes at 13.3v and off/opens at 12.8v. Do I need to get new AGM for 2nd battery to match camper? Thanks for any on-site.

 

[pvstoy]

If the batteries only see each other when you are charging with alternator, then you would be OK.

It is when the batteries are at rest when the age and dissimilar voltage will constantly drag the stronger one down to equalized voltage. In this situation, yes you would prefer to match new batteries.

Sounds like if I understand, you have two new agm batteries in camper. One or two batteries under hood? Confused there.

With isolator between camper and truck will be fine, just Confused what you have set up under hood, single or dual?

 

[Robojeeper53]

Yes there are two batteries under the hood, one for starting the other was an option just to have backup battery in case main starting battery goes dead or to add auxiliary items when engine is off. It has isolator for charging only when engine is running. I have a set of jumper cables to jump back to main battery if needed. Only used once but I was 12 miles back in mountains so was great.

 

[Wandering Sagebrush]

I’m somewhat surprised that your second truck battery is a backup. My Ford trucks (diesel) have all had dual batteries in parallel.

I agree with Patrick, you are fine using the truck to charge the AGMs in the camper.

 

[Jon R]

On the current GM HD trucks the diesels all have two batteries wired in parallel to ensure adequate starting current. The gas HD trucks have an optional second battery with an isolator intended to power whatever accessories you wire to it without draining the starting battery. The trailer connector hot 12 volt positive is wired by the factory to the auxiliary battery.

 

[Wandering Sagebrush]

Jon, thanks for the update. I haven’t had a big gas truck for a long time.