RV Batteries in Parallel

[Medley86]

I know we have some RVers on the forum, so I wanted to see if I could possibly glean some knowledge from y'all.

I just traded in our 2011 23' TT for an 18' Off-Road TT, and I'm setting it up for boondock camping. I was able to keep my battery from the old RV, and it's a 8 month old Type 27 1000 CCA Marine Battery from Duralast. The new RV came with some brand I haven't heard of, but it is a Type 27 as well. Big difference is it's only 575 CCA.

I'm wanting to run the batteries in parallel for additional capacity when we're off grid in the mountains. I know that you have to use similar battery types (AGM with AGM, Gel with Gel, etc.), and as mentioned both are Type 27, but does the difference in CCA cause an issue? Am I going to deal with parasitic draw if I chain them?

no, the CCA difference won't create an issue. CCA is simply the output capability. Time to charge will differ given one battery is 'bigger' than the other but it's still not an issue.

The charge time difference will cause the converter on the rv to overcharge the smaller battery if they are in parallel.

nope. Smaller battery will achieve full charge, then the larger battery becomes the path of least resistance due to it's lower level of charge. Hence current will flow to the larger battery.

Think of two drums, one 10 gallon, one 5 gallon, both at same height with a tube connecting both of them. Fill source is connected to the smaller drum. Small drum fills up and flows into the larger drum via the connecting tube.
electric does the same in this instance.

I worked in a shop for a couple years on motor coaches. Saw several smoke one battery because it was a different size or drastically different age than the other battery wired in parallel with it.

[Pawpaw]

You will be best served by putting two new batteries in it. Then get a BatteryMINDer and it's Quick Connect/Disconnect. Any time the RV isn't in use, hook up and plug the system in. It'll automatically keep both batteries topped off and prevent sulfation.

Years ago, I did that to my father's John Deere tractor. Pop died in 2010 and my mother finally sold the tractor last year. Those 10 year old batteries still fired up that big diesel on the first turn of the key.