Got the coach out of storage for the first time in longer than we'd care to admit. Started right up but I could tell the chassis batteries were down a bit. Got to our destination after a short drive and plugged in to shore power. So far so good.
I started the battery equalizing process just before we left to go out for the afternoon. We got back to a coach that reeked of sulfur - first thought was the holding tanks of course. I eliminated that as the source and pulled out the battery tray to see if the batteries had boiled over and we had acid lying all over the trays. No apparent moisture and all else looked OK. So I chalked it up to the batteries off-gassing during the equalization and the fumes making their way inside through the open windows.
Next morning I started the main diesel to run the air compressor and inflate all tires to spec. When I shut it down and went inside, that funky sulfur smell was back. Hmmm ..... makes no sense. I opened the battery compartment to see the inboard chassis battery (there are 2 group 31s in parallel) spewing steam. I'm no rocket scientist but even I know that a sealed lead-acid battery should not do that
I pulled the shore power connection to stop any charging and waited anxiously as the geyser died down. I wondered what type of explosion I'd get if that hydrogen sparked off.... That one battery was hot to the touch!
I tripped the chassis battery isolator switch and then plugged us back into shore power. The charger was working as it should and house battery voltage was correct. All I could figure was that one battery died with a shorted cell. I replaced both chassis batteries that afternoon and all is well once again. No excess voltage going to the chassis batteries with the engine running or on normal charge.
Is there anything else I should check here? Is this a common type of failure on sealed batteries?