Battery Desulphating/Zapping?

[Things]

Hey guys, I have around 8 of those standard 7Ah SLA batteries here you find in pretty much everything, all of them are brand new, however they have been sitting around for quite a while. They seem to have no issues holding charge, but their internal resistance is through the roof!

I connected them up to a small inverter one by one, and most of them would start out around 12.5V, but upon a 200W load, would instantly drop to around 9V, then jump right back to 12.5V once the inverter shut itself off.

So I'm wondering, has anyone had any experience with those battery zappers? I can grab one from Jaycar for about $40 and try it, but if it's just gonna make matters worse, well I've heard mixed opinions whether it's a good idea to use this on SLA's.

Dan

[dr.diesel]

Not too much you can do since those are gel batteries and not flooded.   Around here you can buy new ones for $17 bucks, not really worth even attempting the zapper.  If flooded batteries you can help them by desulfating them, basically boiling off the plates a little.  From there you can just add back in the water you boiled off, which you can't do with gel.

I'd suggest not bothering, won't make any significant improvement if any at all.

[SeanB]

First of all shake them, if they rattle they are dead and nothing will help. Then take the survivors and charge them with a current of 1A till they measure 14.6V across the battery, and then leave them charging at 13.8V for 24 hours. Then do your load test again, if they fail they are toast and need replacing, or opening up and about 20ml of water per cell, followed by the charging again.

[digsys]

Agree with the doctor. Once they fall below 10.8V for any appreciable time, they'll never get back to what they were.
You can get a buck or two from a lead-acid/sla recycler. Please don't dump them.

[Things]

They have never fallen below 10V, I found them at a reasonable 12.5V and they've pretty much been sitting at that voltage the whole time I've had them, so it's not caused from under voltage or overcharging, simply just from sitting without use for a bit too long.

I think my best bet apart from recycling them is to just charge/discharge cycle them, I've been doing it with one of them and it's showing signs of improvement, but it'll be pretty time consuming. Just a shame they're all basically unused

[digsys]

They have never fallen below 10V, I found them at a reasonable 12.5V and they've pretty much been sitting at that voltage the whole time I've had them, so it's not caused from under voltage or overcharging, simply just from sitting without use for a bit too long.   

In that case, you may be OK. Search the Internet for the "re-juvenating profile" for SLAs. It's basically a continuous sequence of
deep charge / discharge and sometime small reverse voltage spikes. At the very least, do 3 full max charge / discharge cycles.

[Psi]

Yeah, SLA's are pretty crap, there's not much you can do with dead ones except maybe take them to be recycled and get a few $ for the lead.

If you replace them its worth getting a good brand. The cheap ones last 1-2 years where as the good ones last 3-5 years.

[Things]

Waiting impatiently for the day those lithium SLA replacements become a bit cheaper 

What would you recommend for a few charge/discharge cycles? So far I've been charging them at about 4A and discharging with an inverter with a 200W load on it, so probably ~20A. The battery gets warm after a couple cycles of that, though I have the capacity to charge up to 10A.

[dr.diesel]

Waiting impatiently for the day those lithium SLA replacements become a bit cheaper 

Just playing or do you have something specific your trying to power?

[Things]

Waiting impatiently for the day those lithium SLA replacements become a bit cheaper 

Just playing or do you have something specific your trying to power?

I scored a free UPS today - returned item, so figured the battery had failed as usual in UPS's. Just so happens I had all these ones laying around, which I thought would have been OK. But apparently not. So far the one that came in the UPS is performing the best - which isn't good

I've considered throwing them all in parallel and just installing some terminals on the UPS case to connect them all to, that way the load is shared and their high internal resistance isn't really an issue, but I'm a bit worried about it overheating, as it's not really designed to run for long. 56Ah of batteries in a UPS designed for 7Ah would mean it'd run for ages.

[dr.diesel]

Run out to Walmart (whatever your equivalent is) and buy a deep cycle trolling motor battery, they are usually ~100ah for $100 or so.

I've used them in many UPS applications, they work great.  Make sure to match the operating voltage though, most UPSs that have more than one battery are in series not parallel.

[SeanB]

Putting them in parallel will not be very good, one cell dies and it takes out them all. Take them to recycling or use for light loads only, and get a deep cycle battery for the UPS, and place it in an insulated case, as often most UPS units now do not isolate the battery from the input mains for cost cutting reasons. RV battery and plastic box for same are quite cheap, which is what I use, along with a somewhat used car battery. Runs UPS for around 90 minutes on power fail. Too bad most power failures here are a minimum of 2 hours, I need to get a bigger 12V battery next time I go to the scrappie and see any good ones in the pile, or go to the wreckers and get some car batteries. Not paying new prices for them.

[Things]

hmm, I could do, but I don't think this UPS has any thermal protection, and it's definitely not the highest quality thing around, I'd feel a bit risky letting it run at max power for extended (longer than with a single 7Ah battery) length of time. I may be able to add a fan, and maybe some thermal cutoff switches if I could be bothered.