Wednesday, February 8, 2023


Why are RV batteries setting off CO detector?

Dear Gary,
On a recent camping trip, we were connected to 30-amp shore power. During the night, our CO alarm went off. Since there was no stove or furnace operating, I felt the alarm was defective. I did notice the coach battery compartment felt warm. Later when entering the coach from outside, I noticed a foul odor that I couldn’t identify.

We drove the motorhome back to Cincinnati and hooked it up to shore power (30-amp). This morning I went to the RV and the two CO detectors were going off. I opened the battery compartment and found the batteries and cables very warm and the same foul odor. Is it possible that the batteries are producing carbon monoxide poison? —Fred N.

Dear Fred,
The charging and discharging of the batteries will not produce carbon monoxide, but unless charged properly they will off-gas a foul odor consisting of a combination of hydrogen vapors and sulfuric acid. Rapid charging or rapid discharging of the batteries will also produce an abnormal amount of heat – as you’ve noticed.

I’m not sure what brand of CO detectors you have, but it may be possible they are sensitive to the boiling of the electrolyte that is probably taking place at the batteries. It’s also possible the detector has become contaminated or is at the end of its effective lifespan. Check the “Replace By” date tag or label on the back of the detector or in the literature provided. Most detectors will need replacing at about the 7-year mark, but check your date code to verify.

Without having the benefit of running some tests and taking some measurements, I’d hazard a guess that the AC-DC converter is overcharging the battery bank every time you are plugged into shore power. Be sure to keep a close eye on the electrolyte level in each battery in that bank until you rectify the problem. It can literally boil the water right out of the electrolyte, produce heat and off-gas the hydrogen and sulfuric acid. This is the odor, I believe, you are smelling.

In my opinion, many stock charging converters are not sophisticated enough or engineered with circuitry designed for the complete and proper charging sequences necessary for optimal charging of commercial grade deep cycle batteries. Many have a propensity to overcharge the battery bank. I’ve always suggested investing in a dedicated three-step battery charger and allowing the converter to convert and have the battery charger, charge. Multi-stage, processor-controlled chargers can be user-set to accommodate any type of battery so it knows how to charge, when to charge, and at what current and voltage so that overcharging does not happen.

But be sure to verify the integrity of the CO detectors! Never compromise the safety factor! You’ll want to update your detectors if they need replacing. They sounded off for some reason!

gary-736Read more from Gary Bunzer at the See Gary’s videos about RV repair and maintenance.



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3 years ago

I’m having the same issue in my two year old Riverside Retro Trailer. When the battery bank is charging or connected to shore power the carbon monoxide alarm keeps going off even when the propane is turned off at the tanks. I had the propane checked and no leaks as well. I put another carbon monoxide alarm in the trailer and it goes off too when the batteries are charging. Can anyone explain why the alarms are going off when the batteries are charging?

Thanks, Ray

Phil Smith
3 years ago

Shouldn’t the battery compartment be vented to the outside anyway? How are the fumes getting inside the RV?

3 years ago

Good answer, but one other possibility is a dead cell in one of the batteries. This would cause the over charging of all the other cells.

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