I recently found myself troubleshooting a CO alarm on a houseboat. Inside the cabin, a Fluke CO-220 was reading 40 ppm. In the generator engine compartment, the CO level was zero (while the generator was running). We eventually found the source of the CO to be a large lead-acid "house" battery which was warm and leaking:
OL on the display of the CO-220 indicates a value of >1000 ppm CO. I watched it count up through 600, 800, 900 before indicating
Mechanics replaced the batteries, and ensured the battery box was properly sealed and vented. After this, the CO levels were at zero.
Can lead-acid batteries leak carbon monoxide?
This article discusses the chemical reactions of a lead-acid battery, and as far as I can tell there is no carbon involved whatsoever. So I believe the answer here to be "no".
Can a Fluke CO-220 detect gasses other than carbon monoxide?
The CO-220 manual says nothing about any gasses other than CO. In the specifications:
Sensor type | Stabilized electrochemical Gas-specific (CO)
I contacted Fluke and they responded with:
I do not know what gas batteries would put off and the CO-220 has a senor [sic] for CO only. Hope this helps.
I assume the answer here is also "no".
So then, what was going on?