Power To Go: Doubling My RV’s Battery Capacity!

As we were still facing a lack on long term power, the next thing that I planned and followed through on was the addition of two more Interstate Group 27 Deep Cell 12 volt batteries. Now, 6 volt batteries would actually have a larger capacity than a similar 12 volt battery and, when hooked up in series (positive to negative) they create a 12 volt outlet. However, as I already had two 12 volt Interstate batteries we chose to continue with 12 volt. Some of you are likely thinking, Frank, you’re missing out here. New battery technology would offer a much better battery source than the old school technology you’ve described so far. I agree that battery technology is improving at a dramatic rate; but at this point in that development the value isn’t there. If I was working with an unlimited budget, who knows what I would have done, but never in my life have I had that option. This choice is the best value and performance package that I can access. Huge thanks to Kyle at Cottonwood RV and David at Interstate Batteries for helping us sort through this.

When using 12 volt batteries they must be hooked up parallel, as in the positive is hooked to the positive and the negative is hooked to the negative. This maintains the 12 volt output but doubles the capacity. Reading that I did indicated that while you could have the power and negative leads running off of the same battery, that if you had the power on the lead battery then ideally the negative should be off of the tail battery. The rationale being that this forces the battery bank to be used as one whole entity, whereas running them both off of the same battery turns the others into a piggyback setup.  As that sounds logical to me, I used the lead/tail cable system although for the past ten years I’ve always had them run off of the same battery. We could have hooked all four batteries up in parallel to provide 12 volts at quadruple the capacity, but as the original two batteries are over 18 months old there was a concern that they may pull down the new batteries. So the decision was made to create two separate battery banks. Another advantage that I see with two separate banks is that when one bank is run down and I switch to the other, that run down bank can be recharged slowly by the solar panel or by the generator. This will hopefully mean that we will always have a power source on hand.

The decision to double the battery capacity was easy, but it meant that some updates had to happen with the RV. The existing RV house battery on/off switch could only handle one bank of batteries. Rather than having to disconnect and re-connect everything in the middle of the night when one bank runs down, I started searching for a switch that would handle two battery banks. I found that they are plentiful in the boating world. The switch that I obtained allows for Off, Bank 1, Bank 2, and Both. EDIT: originally I said that I’d never use both as that would feed 24 volts to the unit. WRONG! Huge thanks to Joel K who is a marine technician in Bellingham, WA and works with way more complicated setups than what I have. He pointed out that based upon my diagram, Both would still be a parallel setup and provide 12 volts of power and from all 4 batteries. He also pointed out that this is a great setup to use to allow the engine generator to charge up all of the batteries.