AGM Battery Failure Mode?

[sdunn4]

We just replaced our (4) 6-V AGM batteries and upon inspection of the old batteries, the 2 connected in series under the hood (installed side-by-side) show a mirror-image hole right through the casing. The batteries are also bulged out somewhat.

In contrast, the 2 (also connected in series) in the rear and mounted up under the floor by the trailer hitch, were set up end-to-end and show no damage or bulging.

I’m attaching a few pictures in hopes someone can shed light on this apparent failure. We have a 2015 Roadtrek SS Agile; 72K miles and no battery issues until a gradual decline in how long our batteries would stay charged. We keep the RV plugged into shore power over the winter; upstate NY location and outside. We got 7 years service out of the original AGM batteries.

Thanks for any insight; we’d like to avoid this failure in the future. We set our charger / inverter to the new battery manufacturer’s charge and float spec’s and the old settings were very close to the prior installed batteries’ specs.

Steve

[booster]

Heat is a known killer of AGMs along with overcharging.



Many users have posted about the two under the hood failing quickly.


The Roadtrek wiring is also very poor as the batteries get uneven charging due to widely different cable lengths.

[sdunn4]

Thanks; have you ever seen or heard of a failure like this? Of course it’s not, but it looks like biller holes.

[sdunn4]

* bullet, not biller!

[markopolo]

Check whatever holds the batteries in place to see if a bolt or something similar could line up and make those holes.

[booster]

It almost looks like someone drilled holes in them to vent gas to prevent the bulging, maybe. How long have you had the van?

[sdunn4]

We’ve had the van since 2015; purchased new. We did have a mechanic replace the batteries yesterday; he pointed out the holes and said he wasn’t sure if he caused it during the replacement process. Perhaps he did something while removing these 2 batteries- he did mention that they were hard to lift out as there were no handles.

[booster]

Interesting as the batteries have the lift flanges with holes in them. All you need to do is put a small rope or cable through the holes, or even clamp two visegrip pliers onto them.

[Jim Agile]

I believe one of your batteries shorted internally resulting in a localized hot spot that melted through the case of both batteries. The question is what caused the internal short. Are these the original batteries from 2015? Did this occur during the winter? Freezing can cause internal shorts and usually results in bulging of the case. Normally, a fully charged AGM battery should be good to -70 degrees F. Fully discharged batteries can freeze at 20 deg F. Older batteries can fail in a number of ways including develping internal shorts.

[sdunn4]

Thanks Jim,

These are the original 2015 batteries; 7+ years old. We do keep the Roadtrek Agile hooked to shore power during the winter so I believe we wouldn’t freeze as easily. We are only 1 1/2 hours south of the Canadian border though, so we do see some chilly weather. I’m curious as to how others prevent freezing?

Steve

[RossWilliams]

My batteries have done fine here in Minnesota even at -30F. We generally rely on the solar to keep them charged. We also try to give it a long drive occasionally to get the engine fully warmed up which also charged the batteries. The only problem we have had was getting it started last winter. Whether that was a diesel extreme cold problem or the starter battery I am not sure. Maybe a bit of both.

[Jim Agile]

Steve,
Given their age, your batteries may have just failed in a way that resulted in an internal short. I ruined a set of batteries by not paying attention to the charge level during a cold snap in Ohio. I now monitor the charge through a device like the one at the link below. I think you have basically the same rig that I do but a year older. Mine is a 2016 SS Agile. Mine has a cigarette lighter type outlet in the ceiling in the rear. I just keep the monitoring device plugged in there so that at a glance I know the state of my batteries. With shore power connected and the batteries fully charged, the voltage is always 13.5 or greater.

Jim

https://www.amazon.com/Battery-Charg...a-568857243322

[sdunn4]

Thanks for the input; it seems like the internal short sounds likely. Just wondering why / how the short could “jump” across the batteries (as apparently evidenced by the mirror-image holes on the 2 front batteries)? If this can happen, might a fire result? And should these 2 batteries (or any batteries for that matter) be separated with a material that is impervious to the electrical current?

Thanks again for the feedback!

Steve

[rogerstg]

It appears the holes are melted with some evidence of scorching. Perhaps you should reconsider using large AGMs under the hood where the temperatures regularly exceed the 115ish max charging temp. Having the two heat producing batteries side by side compounds the problem. Thankfully, your rig did not catch fire. I would not tempt fate.

AGMs are great in many circumstances. Under the hood is usually not one of them.