Looking for advice on adding leisure battery to diesel Chevy/GMC vans with dual starting batteries.


Long time off-grid vanlife adventurist
GMC Savanas and Chevy Express diesel vans (at least older diesels like my 6.6 Duramax) have one starting battery under the hood and the other along the frame under the driver's side, wired in parallel; doubling capacity but keeping the same voltage.

I'd like to add a 100ah AGM Odyssey house/leisure batt in its own tray alongside the one on the frame (or perhaps in the living space) to store solar power when away from my trailer and its deep cycles and solar setup. I'll have a redundant solar system and charge controllers. I'd like to let it charge when underway, and will isolate it when parked. I'm familiar with how to isolate simply, what gauge wire to use, and appropriate fusing.

My concern is wiring it correctly. Wondering if one place or another is better to splice my house batt into the dual starting batts via isolator, if I chose to let it charge when underway. Do I need to tap in closer to the batt under the hood for any reason or can I simply tap in at the batt on the frame?

Extensive searching over time has resulted in no results from folks who have actually added a house batt to a dual batt starting system.

Anyone here have actual hands-on experience with what I'm looking to do?

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Agreed. I always tap straight off of the main battery. Fuse or breaker at each end of the run. Convenient and safe to keep it separate. Use appropriately-sized wire for the length of run and you're good to go.


We have a dual chassis battery dual alternator and two house batteries.
we charge primarily from solar and have an isolator system to charge the house batteries. However the wiring is very long and very small gauge. In the near future we are switching to a DC to DC charger that will also include a solar charge controller and the capability to charge the chassis batteries from solar as well. As we are looking forward to getting LiPo batteries in the future which last much longer and weigh much less, we could save over 100# with the battery switch. The DC to DC charger can charge the batteries much faster and do a better job of charging them, especially on newer trucks with smart alternatoRS.


Long time off-grid vanlife adventurist
I think I'm going to have to go the DC to DC charger route, eventually. The more I understand my system and what I want to do long-term, the more I find it's the best route.

DC to DC chargers don't combine the systems, but take the excess from the starting system to charge the leisure. These smart chargers sense the different battery types and charging profiles and will boost or dampen down the charge accordingly. The CTEK I'm looking at also includes an aux power input and built-in MPPT solar charge controller.

Until I can spend the money on a good one though (I like the CTEK 250SE), I will not combine the new Odyssey 100 ah AGM to the diesel starting battery system other than temp connection to jump it, if need be. For that, I'll make a lead, wired to the AGM with an Andersen plug at the other end, to which I can connect a long jumper cable with Andersen on one end and jumper clips on the other.

I was hoping to use a simple isolator switch to separate the systems when parked, old school style. The simpler dumb relays and isolator switches, though, have no way to take into account the different ages, types of batteries, and charging profiles, which means one or the other will regularly over or under charge if combined and lead to premature aging and failure. I think this happens a lot more than people know, or perhaps care, about.

Thanks for the replies.
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