Addition of a third House Battery

[HappyCamper]

I have a 2000 Concourse with a two large deep cycle AGM battery bank for house power. I would like to add a third "like" battery to my bank because I predominantly boon dock camp. Has anyone installed a third house battery. If so, where did you physically position the third battery without disturbing the original two batteries and how did you wire it into the current two battery bank?

[caconcourse]

One owner was able to fit three batteries in the battery compartment by removing the tray and using AGM batteries which could be placed on their side. Since yours are AGM already, it might work for you.

[chin_k]

I would wait until the existing batteries reach EOL (end of life) before adding a third, since if their age is not the same, one may end up shortening the life and capacity of the others.

If you still want to do that, there is space to the right of the battery tray that you maybe able to put the extra battery. If you can fit three on the left side, your batteries are too small

[HappyCamper]

Thanks, I have been thinking to place the third batter in the storage compartment on the right of the battery box. Will need to drill a "gromit protected" cable passage hole into the battery area, and wire it into the existing two battery parrallel bank. As the two in use are only 6 months old, I believe I can add a matched third battery without causing any battery life problems. See any potential problems?

[chin_k]

Yes, having more than two batteries will make it very difficult to balance because the weakest one will constantly drain the strongest one in parallel. I really think that you should do some more research on this before proceeding. 6 months is sufficient to make the internal resistant to be different among the batteries that you will greatly shorten the life of one of the batteries, and you will end up with two batteries storing the power, where you started in the first place. You should also look into the different ways to attached your batteries to make sure they are balanced. There are two different ways to attach power to two batteries, and there are maybe half a dozen ways to do it with three, but there is only one way that is balanced.

If you don't care how long your batteries will last, it may not make much difference if they last 2 yrs, or if they last 8 years. But if you are want to get the most out of them, I suggestion you either get two larger batteries to replace the current one, or look into how to make your DC electrical system more efficient, or add more solar if it make sense to you.

[Blue~Go]

If you do hook up three batteries in parallel, I would suggest running the take-offs from opposite ends of the bank. In other words, take the positive lead to your house system from Battery #1, then take the negative lead to your house system from battery #3 (vs. taking them both from #1). This "forces" the draw to go through all of the batteries instead of the other way where #1 takes more of the load, #2 less, and #3 is way in the back trying to see what's going on. This is how I wired my three-battery AGM house bank (getting ready to replace it but it has been in constant use for 9 years so no complaints).

[HappyCamper]

chin_k & Blu-Go, Thanks for your advise. I added the third battery in a parallel bank attaching the house positive draw to B#1 and the house ground from B#3. Thanks again.