How would you add a second house battery?

simplesez · 10-15-2018, 10:05 AM

We use our van more in the winter than the summer. Right now I have a single 27DC battery mounted in a fiberglass box under the floor in the very rear of the van. We have cabinets most everywhere but the rear 16 inches of the van is pretty open. That is where the access to the battery is. We don't have a spare tire, that is where the 2.8k generator is.

I want to add a second house battery since our furnace wastes that single battery pretty quickly.

I know I could easily wire another battery in parallel but can I do one in the under floor box and one on the floor of the van? Seems kinda janky. Considering my space issues what would you do? What other items would you add? Better wiring? Fuses?

Thanks!

simplesez · 10-16-2018, 10:25 AM

Nobody? Anyone have batteries inside their van? Vented box?

**daveb** · 10-16-2018, 10:47 AM

I don't think it would be an issue but it's suggested the batteries should be the same make, size, type, and age when directly bussed together. The size of the batteries and distance dictates the size bus wire probably 2/0-4/0. Really you're not doing a lot different than what you have for the starting system except no separator. Still battery manufactures claim AGM battery can vent in some circumstances.

MorieSugg · 10-16-2018, 12:36 PM

My AGM battery is in the van. Under the bench seat. Positioned sideways to boot. Haven't had any issues.

If I add a second, I would add it alongside. In your situation, I would wonder if there'd be an issue with 2 batteries at (potentially very) different temperatures.

**daveb** · 10-16-2018, 01:19 PM

Quote:

Originally Posted by MorieSugg

If I add a second, I would add it alongside. In your situation, I would wonder if there'd be an issue with 2 batteries at (potentially very) different temperatures.

That is a very good point. I know some prefer to have their house batteries where they can be protected from heat or cold. Both mine are outside on a tray that sits in front of the rear axle. I've never had an issue being outside, but both batteries are always the same temperature.

Sometimes you're better off with one large battery like a 4 or 8D battery if it can be fit in somewhere.

simplesez · 10-16-2018, 01:51 PM

I bought some 0/1 wires, battery box, and two batteries. I'm out about $300 so not bad. Standard lead acid not AGM. I tried an AGM and it didn't seem to agree with my 1996 system.

**daveb** · 10-16-2018, 03:15 PM

Just me but I wouldn't store a wet cell battery inside unless the box lid is air tight and the box has some kind of venting to the outside.

Strange you had issues with AGM batteries. Unlike Gel type batteries, AGM's have fairly similar charging requirements as standard wet cell types. Deep cycle wet cell batteries require keeping the electrolyte level up above the plates so more maintenance.

simplesez · 10-16-2018, 04:04 PM

Yeah I should probably get 2 AGM. I need to look at Costco pricing.

Weinermobile · 10-21-2018, 10:11 AM

This is a good way to mount a second battery without using up inside space:
https://www.torklift.com/rv/hiddenpower

moorefc · 10-21-2018, 10:22 AM

You didn't clearly describe the rear location of the existing battery. My current SMB they are port and starboard back corners in fiberglass wells with covers installed by SMB. They function very well. In your case the genset may be taking up one side.... I've used 12v lead acid in both SMBs. The older, both were under a bench in boxes vented thru the floor. If you could install them in the two back corners, and had room, a very economical solution would be 2 6v golf cart batts. These I believe will fit the Gp27 box except they are about 1/2-3/4" taller. That eliminates the balancing and is, I believe, the most cost effective solution. That said, every year depending on your temperature location you are topping the water level. Good luck on your addition! AGMs are great for their lack of maintenance, but come with a cost.