Dual Batteries - Both primary or isolated?
 

Hello,

I've searched the manual and this forum, but I can't find anything that calls out if the two batteries in my "Truck" [2015 RAM 2500 4X4 Tradesman Cummins 6.7 Turbo Diesel] are both primary or if they are isolated.

I looked under the hood for a battery isolator, but I'm new to diesels and dual battery setups, and I can't find anything that looks like one, but I could be just missing it.

I tow a utility trailer (hooked to 7-plug) with a 12V light in the trailer, and my question is based on the scenario of, if I keep the 12V light on in the trailer, at some point will both batteries die, and will I not be able to start the truck? Or, does the 12V trailer electrical system run off of only one of the batteries, and the battery used to start the truck is isolated from the trailer light circuit, and not run down by the trailer light?

Thanks in advance.

Should be able to trace the + conductor from the drivers side battery straight over to the passenger side battery, meaning they are in parallel all the time.
Unless something changed on the 4th Gens, which is unlikely, the batteries are not isolated from each other.
I think isolating the 2 batteries would be opposite of what you'd typically do say in a boat where you isolate the house battery(s) from the cranking battery and then install a voltage sensing relay to combine them for charging from the alternator.
Yes 1 good battery will light off the Cummins in normal conditions, but I'd imagine anything other than ideal conditions, like cold temps, slight discharge from accessory draw would then necessitate the power of 2 batteries.
So yes, you could drain the batteries by leaving a trailer courtesy light on for a long time.
If this is something you'd be doing regularly it would be pretty easy to install a 3rd battery (where I dunno) and put an ACR (auto charging relay) between one of the primary batteries and the 3rd battery. Then run a separate wire from that battery back to the 12V+ pin on the trailer plug and disconnect the factory 12V+ wire. If your 2012 has the rear floor beer coolers, may be able to stick a battery there, or build a mount off the frame underneath and install a battery in a marine battery box down there.

Thanks Grit Dog. I was afraid of that. I just know I'm going to forget to turn that light off one of these days...

FYI

I had the same question out to the Dealer Service Department that sold me the "Truck".

They got back to me and confirmed what Grit Dog said: the batteries are both primary and not isolated. The dealer recommends getting an isolated third battery for the trailer to avoid running down the "Truck" starting batteries.

Thanks again Grit Dog.