SLA battery refill went wrong?

[cimmo]

My UPS is now about three years old and sure enough, the 7Ah SLA battery is stuffed - it only runs the UPS with a load for a second or two.

Since this UPS is a bit old school with a big wound transformer, it is always dissipating about 30w and therefore the battery has been warm it's entire life. Thinking it has probably literally dried out and with the internet telling me I might be able to restore some capacity by refilling it, I gave it a go. Got nothing to lose, right?
 
The voltage was about 12.0 volts unloaded before I did anything, each cell took about the same amount of distilled water, probably around 100 ml total? After refilling, the open circuit voltage was 11.8v, I started charging at only 100ma and within 10 minutes the voltage had fallen to 10.8v and the battery was getting warm. Oops.

So it's now outside, sizzling away and venting quite a bit of gas, voltage steadily falling (now ~10v) and the battery case is about 40degrees C (ambient plus 25C).

Any idea what went wrong?
Did the internet lie to me?

[Zero999]

You diluted the electrolyte?

Batteries go wrong for other reasons than drying up. If used properly, SLAs don't normally dry up. Any hydrogen released reacts with the oxygen, making water which is released back into the battery.

Why not just replace the battery?

[cimmo]

Why not just replace the battery?

I always planned on replacing it, this was an experiment with the goal to have it as a low capacity general 12v source. It only cost me a little bit of distilled water.

Anyway, once it settles down and stops fizzing, I guess it'll come in handy as a paperweight.

[Halcyon]

I was under the impression that SLAs don't "dry up" and aren't designed to be refilled. Hence the "sealed"?

[Psi]

Yep, they use a gel rather than a liquid. Hence their other name "Gel cell"

I'm not sure of the chemistry but i doubt water will mix with the gel. I think its silicone based.

[tautech]

Replace battery THEN check UPS is charging to ONLY the voltage specified for Standby Cyclic use.

IMHO blame the UPS for the battery failure.

[cimmo]

Replace battery THEN check UPS is charging to ONLY the voltage specified for Cyclic use.

IMHO blame the UPS for the battery failure.

The UPS floats the battery at 13.5v

[tautech]

Replace battery THEN check UPS is charging to ONLY the voltage specified for Cyclic use.

IMHO blame the UPS for the battery failure.

The UPS floats the battery at 13.5v

Sorry correction made to previous post.

Batteries I have here state 13.5-13.8 V for Standby use and I'd think yours was a bit low.

Do you trust your DMM?
Check the charging voltage is at least full wave rectified, preferably smoothed too.
Time to pull out a scope? 

[macboy]

Yep, they use a gel rather than a liquid. Hence their other name "Gel cell"

I'm not sure of the chemistry but i doubt water will mix with the gel. I think its silicone based.

A UPS require high current for a relatively short period of time, and gel cell type SLAs do not do well under those conditions. Instead, AGM type SLAs are used. In these, the electrolyte is absorbed in a fiberglass matt that acts like a sponge. The electrolyte is indeed water based, and it despite the 'sealed' moniker, they do sometimes dry up. But never ever should an SLA be filled or topped up like a standard flooded battery.

[fivefish]

3 yrs is about right for a battery replacement.

[Ian.M]

I suspect too much water was added.  If the battery construction had gas relief passages from each cell to a single over-pressure vent, excess electrolyte would have short-circuited it.

I certainly wouldn't trust a rehydrated SLA battery, nor would I want it near anything valuable . . . . .

[cimmo]

I suspect too much water was added.  If the battery construction had gas relief passages from each cell to a single over-pressure vent, excess electrolyte would have short-circuited it.

I certainly wouldn't trust a rehydrated SLA battery, nor would I want it near anything valuable . . . . .

Each cell had it's own rubber vent cap (that showed signs of moisture around them prior to refilling, this led to speculation that they had dried up). I filled only until the white 'plate' material was covered.
No, this battery was never intended to go back into service in the UPS (there is another one in it now), but it might have come in handy for general use.

I'm still interested in the chemistry involved. It is interesting to speculate how potentially dangerous these things are if they are physically damaged and come into contact with water. This thing was very hot and produced a lot of gas for about six hours, clearly there was a lot of energy there, but it wouldn't supply any appreciable current.
Very curious.

[edpalmer42]

I've tried similar experiments, but didn't have anything like the drama you saw.  I also didn't have much success with rejuvenating them.

If the battery was a 'gel' cell (which is/was a brand name), then you're screwed.  If it was an AGM battery, there was at least a chance of success.  Perhaps if you got to the cells before they dried out, you could add water just like you do to a car battery.  Yes, most 'maintenance free' car batteries would benefit from a drink of water.  It seems that many UPSs overcharge the batteries.  This recharges them quickly, which is good, but dries them out, which is bad.  Once the plates dry out, it's almost impossible to restore them.  The same thing happens to a car battery.

Ed

[CatalinaWOW]

I have found several ways to give new life to these batteries.

1.  As weights when gluing up any number of projects.

2.  As relatively square references when putting together mockups.

3.  As something heavy to throw.

Beyond these the only useful thing I have seen to do with them is to send them in to have the lead recycled.

[tautech]

I have found several ways to give new life to these batteries.

1.  As weights when gluing up any number of projects.

2.  As relatively square references when putting together mockups.

3.  As something heavy to throw.

Beyond these the only useful thing I have seen to do with them is to send them in to have the lead recycled.

And for homemade lead fishing sinkers.

[Red Squirrel]

SLAs will sometimes vent if overcharged/overheated, every time they do this they loose life as they can't really be refilled like flooded cells, well they physically can, but the seal is broken at that point and they arn't meant to be unsealed.  As mentioned it's also more a gel than a liquid so don't think the water does much.

For a small battery like that 3 years sounds about right though, the plates are probably mostly the culprit.  They're just finished.  Plates wear out after a while from sulfation and what not.

[Psi]

You can buy sulphuric acid from the local auto shop for putting in car batteries.
At this point you dont have much to lose by emptying out all the water you added and putting acid back in.

But TBH, pretty much all SLAs are crap. There are a few good brands but 90% of them are cheap china junk and die in 1-2years.