Overcharging/boiling batteries

I couldn't find anything on this when I did the search. We hadn't used our trailer for a year, but keep the charge in the batteries with a battery tender/minder. We have been readying the trailer for a trip down to Tombstone so disconnected the tender and plugged into shore power on Monday. The batteries had full charges. Tuesday evening I went out near the trailer and smelled something funny. The battery box was very hot. I opened it to take a look and the batteries were very hot and smelly. This happened once before, just over three years ago, with the batteries actually exploding in the battery box. We cleaned everything up and purchased new Interstate batteries. Everything seemed fine until now. The batteries were dated 3/2013, but were fully charged. Has anyone had an experience like this? Is it something to do with the converter that isn't recognizing when the batteries are fully charged? Do you think we need to replace the charger/converter? Any help would be appreciated. (I'll have my husband read this before I post in case it doesn't make sense!)

My two cents worth is I really have no idea.... but the charger issue makes sense to me, especially if it has happened before. On the other hand, I assume you have had it plugged into shore power some time in the last three years and it hasn't happened----so why now??? I'm anxious to see what others think.

Rick

All that said----here are some ideas.

The RV Doctor: Ever Nagging RV Batteries

rick

Caryl - It's fairly easy to check your trailer's converter/charger if the batteries are in a full charge state, provided you have a multimeter.

If the converter is going into the "float" state, where it should be if the batteries are fully charged, the voltage across the battery terminals should be close to 13.2V with the converter supplying power. If the batteries have been discharged, perhaps by raising the top, I would expect to see around 14.2V from the converter, as it brings the batteries back up to the full charge state.

If the converter is supplying more voltage than this in these two states, I would suspect it is bad and needs to be replaced.

But, as the excellent article that hilltool referred you to points out, there are battery problems that can give your symptoms too. One that I can think of is an internal short in a battery that will mimic a battery that is uncharged causing the converter to supply high voltage. If you have two batteries in parallel, this will damage the other battery too, since it will be overcharged.

Even a new battery can develop internal problems. They are minimized by using a desulphating battery minder, but they can still happen.

- Jack

Were the batteries deep-cycle?

Yes, the batteries were deep cycle. We purchased two new Interstate batteries from Costco today and installed them. The mobile RV person we have used on other issues came over and checked out the batteries and charger. He says that everything is working fine right now with shore power plugged in. He thinks the charger is pretty weak. We may replace the one that is in the trailer. He likes Progressive Dynamics. That'll be later after our trip next week. We will periodically check the batteries during that time.

One more thought.....

We came up with maybe a common thread for both incidents. Both times that the batteries overcharged and either exploded or leaked, the batteries were older. This last set was 3 1/2 years old. The warranty was only 30 months. We're in Arizona and batteries don't last very long here. I had said initially that the batteries this time were fully charged, but that wasn't with a multimeter test, only what the trickle charger indicated. Maybe because they were older, for Arizona, there was something wrong with one of them, if not both. Anyway, the new ones seem to be fine and the charger isn't trying to overcharge them with shore power plugged in.