Sunday, December 3, 2023


Boiling RV batteries

By Chris Dougherty

Chris Dougherty is a certified RV technician. Here is a letter he received from a reader while he was serving as’s technical editor.

Dear Chris,
boiled fishI have a 50 amp transfer switch. My question is if the power from the converter/charger goes through the transfer switch? I’m boiling batteries and trying to determine if the converter or transfer switch is bad; or none of the above? —James

Dear James,
I have good news and bad news. The good news is that the transfer switch is not involved. The transfer switch selects incoming AC power from the generator or shore power.

The bad news is this is a normal condition for basic ac/dc converters. Simply put, the purpose of a converter is to take AC power from an external source (electric utility or genset) and convert it down to DC. These will frequently apply 13-14 volts to the system continuously, which can lead to boiling the batteries.

The best fix would be to replace that converter with a smart converter system. There are several on the market, including the Xantrex TrueCharge2, the Iota IQ4, the Parallax TempAssure, and the Progressive Dynamics Intelli-power system. They range in price depending on the size and options of the unit, but installation is usually pretty straightforward.

In any case, until you resolve the issue, make sure you keep the batteries topped off with distilled water!




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John Hampton (@guest_2055)
7 years ago

My RV has a “storage” switch to disconnect the batteries. I use a battery charger that automatically switches to trickle charging mode after the batteries are fully charged.

Les Selzler (@guest_1527)
7 years ago

I installed a “kill” switch on the negative side of the RV battery to separate it from the internal charging system. I then use a Battery Tender to maintain it and the vehicle battery switching off from each other time to time. Simpler than replacing the convertor.

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