Weird battery issue.....

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SRGuy

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Joined
Jun 9, 2021
Posts
127
Location
Austin, TX
OK, I have a 12V, RV, deep cycle battery on my rig, in front, in a black plastic, factory installed box. It's 96° out, right now.

This morning, even though we kept the inside at 75°F, overnight, things started heating up, fast, this morning. The 30A AC was blowing less than cold air.

I decided to look around my rig to see if anything was amiss.

When I got to my battery, as above, the black box holding it was very hot. When I opened the box, the battery was burning hot! I decided irrespective of the AC temp, I was going to take that battery out. By the time I got my socket set out, the battery was smoking! Holy Moses! I got it out, and put it on the ground. Two hours later, it's still burning hot. What the??

Time to diagnose: I put my multimeter on the leads that attach to the battery. I was thinking it was being overcharged by my shore powered rig. Nope. No voltage reading. I checked the battery: 12.3V. AOK.

So, what is going on? Is there some runaway chemical reaction heading my battery to a fire and explosion? Am I nuts to take it back home with me?

My next step is to take it in for a diagnosis, provided it doesn't catch fire. I can soak it with a hose, but I'm not so sure that's a good idea.

Come on, experts, please weigh in, here.

Thanks!
 
It would've been useful to see if it was receiving, or supplying current when it was getting hot. That's generally the only way they'll get that hot. One cell can short and potentially boil electrolyte but that wouldn't heat the entire battery and secondarily you wouldn't see ~12V afterward. Practically, they don't have enough energy to get themselves very warm when discharging even at high currents, they'll expend all their energy before they'll get more than just warm. What can happen during charging though is thermal runaway. A characteristic of lead acid batteries is as their temperature goes up, their voltage goes down. A charger connected that doesn't have thermal sensing will just blindly apply current attempting to bring up the voltage, and can overcharge to the point where all the energy goes into dissolving electrolyte and generating heat. So observing the operating conditions when this happens can reveal if this is a battery problem (old, damaged, inefficient) or a charger problem (improper voltage or no thermal control). If electrolyte wasn't vented this battery may still be OK. What I would do is after it cools down connect it back up and watch the voltage and current the converter supplies. It takes a fair amount of power to heat up 50 or 60lbs of lead so any issue with charging will not be subtle. I would want to know this before I committed a new battery to this setup. When the dust settles you can do a timed discharge test and see if the battery was damaged or still operating to spec.

Mark B.
Albuquerque, NM
 
It would've been useful to see if it was receiving, or supplying current when it was getting hot. That's generally the only way they'll get that hot. One cell can short and potentially boil electrolyte but that wouldn't heat the entire battery and secondarily you wouldn't see ~12V afterward. Practically, they don't have enough energy to get themselves very warm when discharging even at high currents, they'll expend all their energy before they'll get more than just warm. What can happen during charging though is thermal runaway. A characteristic of lead acid batteries is as their temperature goes up, their voltage goes down. A charger connected that doesn't have thermal sensing will just blindly apply current attempting to bring up the voltage, and can overcharge to the point where all the energy goes into dissolving electrolyte and generating heat. So observing the operating conditions when this happens can reveal if this is a battery problem (old, damaged, inefficient) or a charger problem (improper voltage or no thermal control). If electrolyte wasn't vented this battery may still be OK. What I would do is after it cools down connect it back up and watch the voltage and current the converter supplies. It takes a fair amount of power to heat up 50 or 60lbs of lead so any issue with charging will not be subtle. I would want to know this before I committed a new battery to this setup. When the dust settles you can do a timed discharge test and see if the battery was damaged or still operating to spec.

Mark B.
Albuquerque, NM
Thanks. I did try to get a reading from the RV end after I removed the battery. At the battery cables there was zero voltage showing up. Was that because the system sensed a no load situation? FWIW, two hours after the battery sat, it was still burning hot. There is a bit of electrolyte showing up on the top of the battery, around the plastic flip-off fill panels. Is this battery safe to travel with? I don't want to put it inside my cab, and I don't have caps for the terminals. I can wedge it in my pu bed, but I'm still concerned about it exploding. I guess if it's cold, tomorrow morning, it should be OK, as long as I wedge it in my bed, where its terminals can't come in contact with any metal strip. If the battery is still hot, tomorrow morning, I'll just consider it a loss.
 
If the battery is still hot hours later it's probably shorted internally.

Here's the gotcha, the converter/charger might be damaged as well.
 
The reason it's staying hot is it weighs a lot and it will take a while for that mass to cool off through air convection. There is little risk in anything exploding. I wouldn't put any flooded battery in the interior of a vehicle as any seeping electrolyte can ruin things. A small storage tote or even a cardboard box to put it in would help protect from leakage and keep the terminals isolated. What is the battery voltage now that it sat a while? One plausible scenario is one cell failed and the converter worked overtime trying to bring 5 cells up to 14V. After resting those 5 cells would be around 10.5V.

Mark B.
Albuquerque, NM
 
As suggested, the converter/inverter charger could be NFG, it is rare but the output may be shorted internally or the output wires (more common). When "things started heating up" did you smell any 'electrical'?
If the output had shorted:
the battery will heat up
the voltage will drop
the HVAC may not have enough voltage to operate, the fan would run slower so no A/C
the reefer may not operate
heat from the converter/inverter charger would rise

What Mark B. says above and if the voltage stays at 12V, which it did as the short shoulda still been there...
You have the battery case, just plop it back in it for transport. If still at 12VDC, I suspect it will be fine, just a reduced life!
What is it you have, converter or inverter? Disconnect the wires from either (or both), check their outputs.
 
Two or three posibilities
First: What converter or power center (if you can't find the convberter) do you have?

Second. Shorted cell in battery


Or a short elsewhere.

Some converters what they feed the battery is a long way from Regulated DC. in fact it's more or less raw, unfilterd, rectified AC

Your meter may read either high or low depending on the design of the meter.
 
I was busy all day yesterday and missed your posts so am reading all of the thread and agree with some of the comments.
When I got to my battery, as above, the black box holding it was very hot. When I opened the box, the battery was burning hot! I decided irrespective of the AC temp, I was going to take that battery out. By the time I got my socket set out, the battery was smoking! Holy Moses! I got it out, and put it on the ground. Two hours later, it's still burning hot. What the??
From what you say it would appear that you have a travel trailer with a single battery in a box that is mounted on the trailer tongue. I'm doubtful that your battery problem would cause the air conditioner to stop cooling but it's possible if your thermostat requires 12V.

An outside temperature of 95° and the black box in direct sun would heat things up but it would be very unusual for that to cause a serious problem. Have you checked the electrolyte levels in your battery recently? If the battery plates are not covered that could contribute to the problem that you have. (Did the air conditioner start to work when you took the battery out?)

Has the battery temperature returned to normal? Keep in mind that if it is sitting in the sun, normal may still be more than you can comfortably hold your hand against. If it has cooled, check the electrolyte levels. If it was boiling, as it seems from your description of things, then there is a high probability that the battery is seriously damaged. You also never mentioned the age of the battery involved? How about an update?
 
I was busy all day yesterday and missed your posts so am reading all of the thread and agree with some of the comments.

From what you say it would appear that you have a travel trailer with a single battery in a box that is mounted on the trailer tongue. I'm doubtful that your battery problem would cause the air conditioner to stop cooling but it's possible if your thermostat requires 12V.

An outside temperature of 95° and the black box in direct sun would heat things up but it would be very unusual for that to cause a serious problem. Have you checked the electrolyte levels in your battery recently? If the battery plates are not covered that could contribute to the problem that you have. (Did the air conditioner start to work when you took the battery out?)

Has the battery temperature returned to normal? Keep in mind that if it is sitting in the sun, normal may still be more than you can comfortably hold your hand against. If it has cooled, check the electrolyte levels. If it was boiling, as it seems from your description of things, then there is a high probability that the battery is seriously damaged. You also never mentioned the age of the battery involved? How about an update?
UPDATE: The battery is shot. In keeping with expert service and sales, the place where I bought the battery never bothered to scratch off the month and year circles on the battery. I believe it's four years old. I'm sure I have the receipt in my RV folder. This morning, the battery was swollen, and had cooled down. It read 4.3V on my multimeter.

I had an epiphany, of sorts: I have never used my battery as my sole power supply. I don't ever boondock. I only use my battery when I hook up my air pump to top off my tires. I have a smaller 12V that I can use for my pump. It's easy to carry, unlike that deep cycle monster. I can carry my battery tender. Goodbye, onboard battery. I will cap the battery cables in that black battery box. They're taped, right now, but no tape stands up, for a long time, to the blistering Texas Summer Sun!

Thank you, everyone who weighed in, here. Your input was greatly appreciated, no lie!
 
UPDATE: The battery is shot. (...) Goodbye, onboard battery. I will cap the battery cables in that black battery box. They're taped, right now, but no tape stands up, for a long time, to the blistering Texas Summer Sun!
If this is a trailer, you can't get rid of the onboard battery. It's legally required to supply power to the trailer brakes via the breakaway switch if the trailer ever becomes disconnected from the tow vehicle. Just replace it every couple of years as an ongoing maintenance item.
 
If this is a trailer, you can't get rid of the onboard battery. It's legally required to supply power to the trailer brakes via the breakaway switch if the trailer ever becomes disconnected from the tow vehicle.
And it is also a safety item! The other thing to keep in mind is that even when your refrigerator is on propane it requires 12V power to operate the controls so without a battery the refrigerator will not work when disconnected(without shore power) or when you are stopped with the tow vehicle engine off.
 
And it is also a safety item! The other thing to keep in mind is that even when your refrigerator is on propane it requires 12V power to operate the controls so without a battery the refrigerator will not work when disconnected(without shore power) or when you are stopped with the tow vehicle engine off.
I never use propane for the fridge. I will get a battery for the trailer brake, though.
 
If this is a trailer, you can't get rid of the onboard battery. It's legally required to supply power to the trailer brakes via the breakaway switch if the trailer ever becomes disconnected from the tow vehicle. Just replace it every couple of years as an ongoing maintenance item.
Thanks. I will do that. I'd like to avoid another deep cycle marine/RV battery. My 20' flatbed uses a very small 12V battery for the brake. My RV battery had two leads attached to each terminal. I believe the thin leads go to the trailer brake. With that in mind, I may try one of the small 12V batteries, and test the brake using it. I can line test those small leads for continuity with the trailer brake.
 

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