Boiling SLA battery

[Quirts]

This weekend, after a long hiatus we took our travel trailer out for a short trip. Connected to shore power at the campground and late in the second day came back to our rig with a big puddle under the battery, steam venting, and nasty hydrogen sulfide smells. Clearly the battery is overcharged. So, is it just a bad battery ( only a few years old and barely used - but that could be the problem- barely used) or is there something wrong with the trailer’s charging system? Reluctant to connect another battery until I understand what happened. Thanks!

[dsol]

Lots of possibilities and there are some pretty knowledgeable battery experts who contribute (not me unfortunately) regularly but if I had a guess it was the battery and not the charger.

Your inverter has three charge modes and the first is called bulk where it puts out about 14.4 volts for about 4 hours, It then drops back to absorption mode which is 13.6 volts and once topped off it goes into float or trickle mode after some period of time. Bulk mode can be skipped or shortened by the inverter if it detects a sufficient charge on the battery or batteries too. But even a severely discharged battery only gets a max four hours in bulk mode based on the safety design of the inverter.

A healthy battery should be able to handle 14.4 volts for 4 hours even if full but if your battery went flat and sulfated that could cause problems.

I suspect your battery was damaged and sulfated and the bulk charge cooked it further.

I also suspect a new battery will be fine. However, there is a chance that your inverter is bad and might have put out more than 14.4 volts but I have never heard of that. Usually when they go bad they don’t put out sufficient voltage as opposed to too much.

If you put a new battery in your rig I would put a multi meter on the terminals when first plugged into shore power then check it about 5 hours later. At first it should be 14.4 volts or so due to the charger then it should drop to 13.6. If it stays on 14.4 longer than about 4 hours there is likely a problem with the inverter.

But my bet is you had a bad battery.

[ewarnerusa]

You gotta take batteries out and maintain, or at least completely disconnect them, if you're going to store the unit. If camper was sitting for a long hiatus with battery in place and connected, it is most likely totally dead. If disconnected, possibly dead if the hiatus was long enough. Once dead, who knows what happened to the water within. It could have frozen solid and/or partially or fully evaporated. When you began to charge it via the onboard converter (not inverter, that does the opposite) the partially filled or dry battery self destructed?

I agree with dsol that the converter doesn't seem like the culprit, I think the battery was compromised and caused problems when charge was applied.

[dsol]

Originally Posted by ewarnerusa

You gotta take batteries out and maintain, or at least completely disconnect them, if you're going to store the unit. If camper was sitting for a long hiatus with battery in place and connected, it is most likely totally dead. If disconnected, possibly dead if the hiatus was long enough. Once dead, who knows what happened to the water within. It could have frozen solid and/or partially or fully evaporated. When you began to charge it via the onboard converter (not inverter, that does the opposite) the partially filled or dry battery self destructed?

I agree with dsol that the converter doesn't seem like the culprit, I think the battery was compromised and caused problems when charge was applied.

Yes, ewarnerusa is correct. It is a converter not inverter as I stated. I think I have been reading too much about battery systems to power the AC system in RV’s lately.

[ewarnerusa]

On re-read, I see that OP said SLA (sealed lead acid) battery. I was thinking Flooded Lead Acid, but still the same care must be taken if being left uncharged. It is highly unlikely any water evaporated from the battery during storage since it is sealed. But severe discharge would still kill the battery I think and possibly result in the symptoms presented in OP.

[persistent]

Lots of good advice. You probably needed new batteries before you started this latest trip. Violent lead acid battery failures are typically caused by internal short circuits. A plate or piece of a plate may have broken off and shorted a cell. Charger then provides high current. High temperature makes steam which explodes case.

Lead acid batteries must be stored fully charged. Charge for 14 to 18 hours. Abused batteries may benefit from 24 hours charging.
Disconnect battery from the system.
Fully recharge before voltage drops below 12.4 volts.
Monitor battery terminal voltage frequently until you know how long your batteries will last.

Flooded cell or SLA batteries in good condition may last up to 6 months.

[dsol]

OP also stated he came back to a puddle of water under the battery and it was venting gas so I don’t think it was sealed any longer and may have been compromised prior to this charge. I am guessing it was likely compromised already.

SLA’s still are designed to vent gases when charging but not supposed to lose water—or what is actually battery acid, however they do fail and anything can happen.

Properly maintaining RV batteries is not difficult but does require constant attention. They need to be topped off monthly or so and if someone leaves them on a constant charge—even a trickle charger they will be damaged from overcharging and lose capacity over time. And they still will fail for random reasons from time to time as well.

My last rig had built in solar charging but all that did was overcharge my batteries as it never cut off and so I have “full” batteries every time I used it but they had terrible capacity because they were just slightly boiling off water over time but you couldn’t tell.

[User13744]

“Long hiatus” ? How long is that, about? That may be a factor. Was battery stored outside?

High temperatures are brutal (permanent sulfation) and on the other hand, battery electrolyte will freeze at around +20° F. when significantly discharged. A 50% charged battery might freeze up partially at about -5° F. below zero, something like that.