Tuesday, June 6, 2023


How to add RV batteries

gary-736Hey Doc,
I recently purchased a used Class A Newmar coach. Where do I find out what rating of battery needs to be used for replacement? The specific gravity on the existing batteries is low and after charging, is not coming up. The batteries are weak after only eight hours of using a very light load. They are five years old. I have no clue as to what amp-hour I should be using. —Rich W.

Hi Rich,
You can measure the battery cases of your existing batteries to determine the amp-hour rating. Most battery suppliers will have a chart indicating the amperage rating based on the physical size of the case.

But it’s always been my advice to carry as many batteries as the space and your wallet will allow. You can never have too much battery capacity. Many motorhomes use Group 27 (or larger) batteries for their auxiliary DC power. Some go with 6-volt batteries wired in series. Be sure to have your existing batteries tested properly before condemning them – though, at five years, they probably have indeed expired their useful lives.

Put as many Group 27s in there as can fit. You’ll want the highest amperage storage capacity as possible. As an example, two Group 27, 12-volt batteries wired in parallel will equal about 210 amps of storage capacity. Two Trojan T-105, 6-volt batteries wired in series will yield about 225 amps of storage. If you can fit three or more Group 27 12-volt batteries, then go for that. When using 6-volt batteries they must be added in pairs. But do the math – four Group 27s in parallel will provide 420 amps or so, but four T-105s will provide 450 amps total, and with a slightly smaller footprint.

More is usually better! You may also want to consider an upgrade to AGM batteries if you plan on extended dry camping excursions. Lots of options to consider! 




Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.



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Thomas Bender
5 years ago

Almost $500 for 6 volt batteries forget it I’ll stick with the 12 volt 27

Tommy Molnar
5 years ago

I WISH I could add more batteries to our travel trailer. We currently have two Trojan T-145’s and they do fine. But, as Gary says, you can never have too much power. There just isn’t any room for more, and we’re tipping the max weight on our trailer anyway. We have 375 watts of solar on the roof as well so we do ‘alright’, but in the winter months more of everything would definitely be better.

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