AGM Battery Cooked !

[Doodles]

The other day I started to smell something unusual in the boat and it turned out to be one of my house batteries. I have two house and one engine all Group 27 AGM's of an unknown age. The battery was pretty hot, sides bulging out and you could hear it boiling! Got it disconnected and out of the boat ASAP.

Now I'm wondering why? I have been at the dock for some time and on shore power. The charger is an older one (came with the boat as did the batteries) and the manual suggest it was not designed to accommodate AGMs, but it was GEL batteries and set for them I think. So, I'm wondering if the charger was the problem? Any thoughts?

I'm planning on replacing everything at this point. New charger and 3 new batteries. That way I will know going forward what I got.

[noelex 77]

You can do some basic tests on the charger to see what voltage it is maintaining the batteries.
You are wise to consider faults in both the batteries and the charger (also check your other charging sources such as alternator and solar if you have them), but the fault probably lies with the battery dropping 1 cell and the charger is likely to fine. If 1 cell becomes shorted the other 5 cells are overcharged (say 14.5 into 5 cells instead of 6) resulting in the kind of battery problem you describe.


Charging AGM batteries at a Gel setting is not perfect, but main effect will be to slow the charging rate down a little. On some chargers the flooded setting is OK with AGM
I would measure the chargers regulation points and see how closely they match the battery manufactures recommendations. if you want to leave the charger connected it should have at least 2 regulation points. (absorption and float)

It seems a shame to throw away what may be a good charger, when a few simple tests will tell you how its performing.

[Ex-Calif]

Are you sure it is a charging fault and not a discharge fault? i.e. A short somewhere in the house?

Be a shame to put all that new equipment in and fry it again.

It probably is a single cell or single battery failure but you gotta ask why? You had a potentially pretty dangerous situation on your hands.

[Doodles]

Originally Posted by noelex 77

You can do some basic tests on the charger to see what voltage it is maintaining the batteries.
You are wise to consider faults in both the batteries and the charger (also check your other charging sources such as alternator and solar if you have them), but the fault probably lies with the battery dropping 1 cell and the charger is likely to fine. If 1 cell becomes shorted the other 5 cells are overcharged (say 14.5 into 5 cells instead of 6) resulting in the kind of battery problem you describe.


Charging AGM batteries at a Gel setting is not perfect, but main effect will be to slow the charging rate down a little. On some chargers the flooded setting is OK with AGM
I would measure the chargers regulation points and see how closely they match the battery manufactures recommendations. if you want to leave the charger connected it should have at least 2 regulation points. (absorption and float)

It seems a shame to throw away what may be a good charger, when a few simple tests will tell you how its performing.

I'm a real novice with this stuff but my reading says the AGMs require a very specific charge regime and I've never been too comfortable with his old charger since it apparently pre-dates AGMs. I'm not sure I trust myself to determine if it is doing the job correctly. I'd just feel better with a new charger designed to handle AGMs.

Originally Posted by Ex-Calif

Are you sure it is a charging fault and not a discharge fault? i.e. A short somewhere in the house?

Be a shame to put all that new equipment in and fry it again.

It probably is a single cell or single battery failure but you gotta ask why? You had a potentially pretty dangerous situation on your hands.

By "short somewhere in the house", do you mean the house battery? Why wouldn't replacing the battery take care of that? What other kind of discharge faults could cause this?

You had a potentially pretty dangerous situation on your hands.

... yea, sure scared the sh#t out of me!

[Seahunter]

Originally Posted by Doodles

...Now I'm wondering why? I have been at the dock for some time and on shore power. The charger is an older one (came with the boat as did the batteries) and the manual suggest it was not designed to accommodate AGMs, but it was GEL batteries and set for them I think. So, I'm wondering if the charger was the problem? Any thoughts?

You're lucky you were there, as an AGM runaway can be very nasty. It sounds like a charging error, maybe they went into EQ automatically. It's not good to mix battery types as charging patterns and points are different and many chargers are not adjustable enough to to the job. Many AGMs can't be EQd, even though they can take a heap of input charging voltage, when they run away they do it quickly.

[noelex 77]

Originally Posted by Doodles

I'd just feel better with a new charger designed to handle AGMs.

No problems. Let me know if you change your mind and I can talk you through what the charger should be doing.

[noelex 77]

PS make sure you are wearing eye protection when installing the new batteries. I have seen a few terible eye injuries

[hellosailor]

Doodles, unless your batteries were home-built as a science fair project, you can find out exactly how old they are by looking for the date code. This is either embossed, stamped, or printed onto the battery housing itself--not the label--for warranty verification. By all manufacturers. Often they get clever and slap the paper label OVER this so the consumer can't tell how long the battery has been sitting on the shelf. And sometimes you need to call the maker to translate the code, i.e. "25109" could mean the 251st day of 2009.
But you can find out how old they are, and if it is 6-8 years...that could just be all they were going to do.

[Doodles]

Originally Posted by hellosailor

Doodles, unless your batteries were home-built as a science fair project, you can find out exactly how old they are by looking for the date code. This is either embossed, stamped, or printed onto the battery housing itself--not the label--for warranty verification. By all manufacturers. Often they get clever and slap the paper label OVER this so the consumer can't tell how long the battery has been sitting on the shelf. And sometimes you need to call the maker to translate the code, i.e. "25109" could mean the 251st day of 2009.
But you can find out how old they are, and if it is 6-8 years...that could just be all they were going to do.

Thanks, I'll check this out.

[Ex-Calif]

Originally Posted by Doodles

I'm a real novice with this stuff but my reading says the AGMs require a very specific charge regime and I've never been too comfortable with his old charger since it apparently pre-dates AGMs. I'm not sure I trust myself to determine if it is doing the job correctly. I'd just feel better with a new charger designed to handle AGMs.

By "short somewhere in the house", do you mean the house battery? Why wouldn't replacing the battery take care of that? What other kind of discharge faults could cause this?

... yea, sure scared the sh#t out of me!

It would have to be a fairly obvious short on the primary cabling. A remote possibility because the question begs why not both batteries but I would check the primary cables thoroughly for chafing before putting in new equipment.

[Bash]

I had that happen once with a Gel D-4. Battery was removed for me by the local fire department because it had gotten too hot to handle with regular work gloves.

What happened in that case is that the battery had shorted internally after beating to weather in some particularly nasty chop.

[bstreep]

We had an 8D do the same thing about a year ago. We were thankfully on board.

We replaced with new Lifelines. Before spending big $$ on batteries, I'd also check out the existing system and I'd probably also replace the charger.

As pointed out above, since it was just one of the batteries, I'd suspect the battery rather than the system. If it's over 5 years old, it was probably "time". You can get a lot more life out of them than that, but you HAVE to take care of them. I didn't on mine, and the prior owner obviously was clueless.