Monday, June 5, 2023


Charging 6-volt RV batteries


gary-736Hello Gary,
Is there a way to charge my two 6-volt batteries with a regular stand-alone battery charger? If so, how would you hook up the positive and negative charger clamps —George

Hi George,
I’m going to assume you are referring to a stand-alone battery charger that is 12 volts only. I mention this because some shop chargers are equipped with a 6-volt output option as well as 12-volts DC. Since all DC components on RVs operate on 12 volts (water pump, fans, lamps, etc.), your two 6-volt batteries, as installed, are still set up to produce a 12-volt final output. The only difference is the connection between the two batteries. 

At the basic level, two 6-volt batteries are wired in “series” and two or more 12-volt batteries are wired in “parallel” in order to produce 12-volts final output. Take a look at the diagrams here: two 6-volt batteries (above) and two 12-volt batteries (left). The final output that provides battery power to the components in the RV is still 12-volts DC. Therefore, both configurations can be charged by any 12-volt battery charger by simply connecting the charger’s red cable clamp to the “plus” 12-volt terminal lead and the black or ground cable clamp to the negative terminal, as shown here. 

But a word of caution! Notice on the 6-volt battery diagram, you must know which battery feeds the positive voltage to the RV and which battery represents the negative connection. If your series connected batteries look similar to those depicted here, then all you do is connect them as shown. If yours are wired differently, that requires further investigation. Bottom line: 12 volts is still 12 volts. You do not want to connect either battery charger lead to the posts that make the interconnection between the two 6-volt batteries.

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




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5 years ago

Like your idea, but you may be making it too difficult.
Years ago I put a small ( 2 gallon? ) pressure tank with a bladder from Home Depot in my ’89 Southwind. Great improvement! Two flushes without the pump ( under the bed ) running in the middle of the night. Rinse dishes with out cycling the pump on and off for each squirt of water. Better shower. Keeps the pump from cycling for every water draw. Mounted it outside underneath near the pump. Doesn’t matter where it is in the system. Took it with me when I moved into my Monaco DP. Best water system improvement ever.

Ray Mayfield
5 years ago

Hello Gary,
I have a question about the freshwater system. Is there a logical reason why companies that manufacture RVs’ do not install a pressure tank anywhere in the plumbing system downstream of the pump? I have been contemplating building and installing a pressure tank in our motorhome. A simple design carefully constructed from 6 inch pvc pipe and mounted in a corner or closet would provide both reservoir and pressure without adversely impacting any component of the water system. It would provide a much more pleasant showering experience. At approx. 1.5 gallons per foot, a 4 ft. section of schd 40 pvc pipe securely mounted vertically and valved on both ends would provide sufficient pressure (40 psi pump discharge) with minimum weight and a neglible footprint. It would actually increase the water system capacity by 4-5 gallons. Is there any reason unknown to me why a pressurized system would not be desireable? It should make no difference to the water system when attached with a regulator to a pressurized delivery system, and would be wonderful when boondocking. i have yet to see a pressure tank in an RV freshwater system (towable or motorhome) and I find that perplexing.
Thank you,

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