Adding Water to VRLA (SLA) batteries?

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PJD
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Adding Water to VRLA (SLA) batteries?

Do VRLA batteries ever fail simply due to drying out or outgassing of their water? And if so, can a small amount of distilled water added to each cell rejuvenate them? I'm thinking of attempting this with some poor-performing "silicone" batteries...

reikiman
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Yeah, I think that's a

Yeah, I think that's a possibility. On the old VV.com site we'd had some discussion around this idea. What I gathered is...

A charger can "overcharge" a battery pack and as you suggest that could lead to offgassing. The builders of large EV's often use flooded batteries where you have to add water every so often, and one thing they do for maintainence is to occasionally purposely overcharge the batteries so that the electrolyte boils and the sulfur is removed from the plates. Of course that leads to decreased liquid and you have to add liquid.

But a sealed battery if you lose liquid you can't replace it. I suppose this might be different for a gel battery.

A couple people had made some postings about opening their sealed batteries and adding water. But I recall the results being unimpressive. They found lower liquid levels but I think they didn't get any improvement afterward.

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PJD
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I have read that VRLA

I have read that VRLA battteries use a catalyst that recombines any hydrogen and from outgassing during charging this process is 94% efficient, so the electrolite soaked glass-mat separators use for VRLA batteries don't lnormally lose any water unless badly abused.

But the silicone electrolite may be different.

It would be ironic if those people who have probably thrown their e-max's with defective-from-the factory batteries off a cliff only needed to have added a bit of water to them...

mf70
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Re: Adding Water to VRLA (SLA) batteries?

With AGM batteries, it is indeed possible to add water. In my experience, it makes perhaps 20% difference (maximum). I suspect that once they've dried out, irreversable sulphation sets in.

I would be surprised if your silicone batteries could be helped, though. In my understanding, the Guening "silicone" process is another gel cell, and added water would just sit on top of the "silicone" mass. (Of course, glass (as in AGM) is mostly silicone: "Common glass contains about 70-72 weight % of silicon dioxide (SiO2)." sayeth Wikipedia.)

I have read that AGM's have a catalyst that recombines the excess H2 and O2 gas, but I've never seen any such structure when I've bandsawed a dead battery apart.

I'd be interested in seeing the fill on the Guenig battery if you felt like slicing one open.

Mark

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Re: I have read that VRLA

When the charge voltage gets to be about 14.5-15 volts for an AGM battery usually you can hear "bubbling" if you listen real closely. If you raise the voltage higher they will bubble and vent, sometimes making louder venting noises. The fact that they are called VRLA (valve regulated lead-acid) means they have a valve to keep the battery from venting unless the pressure gets too high.

In my experience, it makes perhaps 20% difference (maximum). I suspect that once they've dried out, irreversable sulphation sets in.

I haven't been able to revitalize UPS batteries, maybe this is the reason..., i.e., they sat dry too long.

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Re: Adding Water to VRLA (SLA) batteries?

When the charge voltage gets to be about 14.5-15 volts for an AGM battery usually you can hear "bubbling" if you listen real closely.

To me it looks like an AGM battery shouldn't bubble: AGM's have no free liquid - see Battery FAQ - AGM. I would also guess you can't add liquid to a gel battery.

If you are "bubbling" any type of sealed battery, wouldn't that be overcharging it? (since you can't replace lost water).

mf70
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Re: Adding Water to VRLA (SLA) batteries?

The bubbling is coming from the plate-electrolyte boundary, as water is electrolytically decomposed into hydrogen and oxygen. In an AGM battery, the electrolyte is liquid, and will bubble.

There is no "free" electrolyte in an AGM, so a broken battery won't bleed electrolyte, but the working surface is a liquid. You can see the effect if you put a soaking wet paper towel against a piece of glass. The glass is exactly as wet as if you just poured water on it.

And yes, if you can hear it fizzing, an SLA is being overcharged.

Your FAQ link had an interesting term for the re-composition process:

the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water

Anybody care to explain that?

antiscab
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Re: Adding Water to VRLA (SLA) batteries?

most Gel/AGM batteries have a recombiner that does indeed convert the hydrogen and oxygen back to water (and heat).
It doesnt capture all of the hydrogen and oxygen, since the seals arent perfect, and the reaction can only happen so fast.
So there is still capacity loss when you overcharge a AGM or gel battery.

The original question is a blast from the past though....any1 else been seeing threads from 2007 being commented on recently?

Matt

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