Why are RV batteries setting off CO detector?

gary-736Dear 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 seven-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! 

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




7 Thoughts to “Why are RV batteries setting off CO detector?”

  1. Mike Ackerman

    We also had a ‘ hot ‘ battery set off the CO2 sensor. It turned out the ground connection on the hot battery had come loose.
    The sulfuric acid smell was awful. We had to open the RV and put a fan near the battery box in the step well to help exhaust the fumes.
    After tightening the ground connection on the hot battery it cooled and the smell finally dissipated.
    BTW: We had to disconnect the CO2 sensor overnight until the battery cooled.

    1. John

      It’s a CO (carbon monoxide) sensor, not a CO2 (carbon dioxide) sensor. CO2 is what you exhale when you breathe.

  2. peggy coffey

    My CO detector goes off when we spray anything, Febreeze, Lysol or Pam. I dont know why.

  3. Ken

    Batteries with a bad cell typically cause the charger to continue charging and boil the batteries. The off gassing of hydrogen from being overcharged will always set off any carbon monoxide sensor. It’s called cross interference and is a known factor. The smell is the battery acid being vaporized. The original poster has a bad battery most likely, or less likely a bad charger. A hydrometer will quickly show the bad cell(s).

  4. JB

    Another helpful solution is to install air vents in your battery compartment.I did this after buying a new fifth wheel which had the batteries installed in the front storage area with only a cheap plastic box and hose for ventilating gas fumes.I simple bought a matching vent as the one the manufacturer installed for the hose and installed it on the opposite side of the compartment thereby allowing fresh air into the battery compartment.No more smell. And if you have battery boxes with a vent hose,make sure battery boxes have a good seal..or fumes will escape the box.

  5. Darrel

    When batteries go bad they will get very hot and out gas. Touch the batteries – do they feel hot? If so, disconnect the battery(s) and replace them. May want to upgrade your charging system at the same time.

    1. frater secessus

      > I’ve always suggested investing in a dedicated
      > three-step battery charger and allowing the converter
      > to convert and have the battery charger, charge.

      Doesn’t have to be either/or. There are aftermarket converters with smart charging. I setpoint configurability is critical for my uses, but configurable smart-charging converters are $$$.

      So I built a DIY smart converter using a 24v power supply and a spare MPPT controller. Got the idea from this video:

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