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pstadt · 18-01-2014, 15:18

I have three house batteries on our boat (which is winterized and in the water) and have kept the charger/inverter on. There is minimal draw - LEDs on the breaker panel, digital clock on the radio, etc. Batteries have been registering "full" on every periodic check of the boat, even today (01/18/14). Batteries are going on three years old this spring.
While checking the starboard engine compartment today, found the aft battery of the three had exploded, with no apparent flames or damage, other than acid on most everything. See pic.
From what I can tell, they are a European brand AGM 12V120a (20hr). The remaining batteries appear OK. I've isolated the bank and shut down the inverter until I can clean up and replace the ex-battery. I wiped up everywhere (did in a sleeve on a favorite nylon jacket in the process) and got the battery ready to pull.
We did have a sharp cold spell about two weeks ago, single digit (F) for about two days, followed by a warm spell (55F). Back down to freezing temps again now. I've watched videos on how AGMs are built and operate and one on checking the voltage individually on banked batteries but couldn't find any on what causes the type of casualty we experienced today.
So, jokes and pokes are welcome, but please offer a real conclusion as to why this may have happened.

Thanks!

Pat

Teknav · 18-01-2014, 15:25

Two probable possibilities; hydrogen buildup formed from the battery's acid, or liquid freeze resulting in the expansion of the battery's case (as if it was like an explosion).

Mauritz

brazenarticle · 18-01-2014, 15:28

In an attempt to discard the obvious - perhaps too much tension on that strap? Was it tight enough to change the geometry on the battery top so pressure was all applied at one spot?

**HappyMdRSailor** · 18-01-2014, 15:42

Quote:

Originally Posted by brazenarticle

In an attempt to discard the obvious - perhaps too much tension on that strap? Was it tight enough to change the geometry on the battery top so pressure was all applied at one spot?

I was going with the freeze thaw cycle.... but maybe the case gave in with the tension while the case dimensions changed due to the temp change?

pstadt · 18-01-2014, 15:43

Thanks Teknav and brazen article. For brazen: while I first thought "no way" on your suggestion (as that strap has been in the same tension for the past three years)…that really makes a lot of sense (as that strap has been in the same tension for the past three years). All friction aside, the forward battery (the adjacent one within this strap) should also have felt the same compression at the edge, so I'll give this one a good check over when removing the bad one.
Teknav: Good suggestions - from what I've learned today there should be little Hydrogen build up in an AGM (if it's in good working order) and the 65% acid/35% water solution should have a very low freezing point..but I won't discount the possibility of either and I thank you for your suggestions.

socaldmax · 18-01-2014, 15:43

This is entirely speculation on my part, but here goes.

I think the liquid acid absorbed in the glass mat froze and expanded, cracking the casing of the battery. The only reason I can think of as to why only that battery cracked and not the other 2 is it's location, at the end of the compartment where cold air might have seeped in and made that battery colder than the other 2, which were not close to the source of the cold air. The cold air would have crept in at the edge or where ever there was a gap in the hatch seal and filled up the compartment from the bottom. Since the single digit cold snap was only for one day, it warmed up before enough of the cold air could enter to make all 3 batteries the same temp.

Another theory is that teh cold snap did it, but that one battery had a small defect in the casing that allowed only that one battery to crack.

glenn.225 · 18-01-2014, 15:59

Looks like a significant event, a lot of damage. I have seen several frozen batteries burst and others "explode" (although it's more like pop) when trying to boost.
Could the battery have been weak enough to freeze? Although that sounds odd with charger hooked up. One scenario where I could see this happening is shore power went off, battery froze, power came back on, battery burst.

But for sure you will need a new battery

d design · 18-01-2014, 19:11

Do you have a wife?

colemj · 18-01-2014, 19:14

Did your charger have a temperature compensation probe? If so, it is likely the compensated charging voltage was well over 15V at that temperature. Perhaps this boiled the sparse water out and caused a cell short?

Mark

**Hud3** · 18-01-2014, 19:19

Battery acid in a healthy battery is around 30% H2SO4. The freezing point at that concentration is around -30* C. I can't image it got that cold in your boat.

p.s. I don't carry this stuff around in my head--I Googled it.

colemj · 19-01-2014, 06:24

If the battery became discharge for any reason, the acid concentration would be very low and the freezing point significantly higher.

Mark

Zednotzee · 19-01-2014, 06:32

Quote:

Originally Posted by colemj

If the battery became discharge for any reason, the acid concentration would be very low and the freezing point significantly higher.

Mark

That's what I suspect too. Even a slight discharge can significantly raise the freezing point of a battery.

Lots of good battery info at http://batteryuniversity.com/

perchance · 19-01-2014, 06:51

A discharged battery will freeze and split the case. A fully charged battery is best stored in the cold as it slows down the rate of self discharge but should be monitored as to state of charge. A trickle charger left on during storage will keep it topped up.

AfterHoursNLCT · 19-01-2014, 07:17

Quote:

Originally Posted by perchance

A discharged battery will freeze and split the case. A fully ....

If the battery did freeze and split the case, the acid would have just flowed out the crack and down the side of the battery. How did it get all over everything other than having some sort of explosion???