Testing gelcell SLA batteries

Thread Starter

Wendy

Joined Mar 24, 2008
21,906
I have a couple of old gel SLA batteries I've mixed up. Is there a way to test and separate the good ones from the bad ones? I've not after something fancy, just a quick and dirty test.

I have a new car charger that has a gelcell menu option that I can use.
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,906
I'm thinking more along high internal resistance. I suppose I could charge them then discharge them using a 12V car light bulb and measure duration.

While I haven't measured them, I am assuming they have normal voltage. One of them sat in a UPS for well over a year.
 

SgtWookie

Joined Jul 17, 2007
22,210
Bill,
Are you certain that they are gel-cel?
You may want to look up the datasheet. AGM batteries have been out for awhile now.

Gel-cell batteries will have their capacity permanently reduced if they are overcharged; the breaking down of the water into hydrogen and oxygen gases makes voids in the gel that are permanent.

I suppose you might be able to get the bubbles out by using a centrifuge, but that would also collapse the plates.

You might want to use an automotive 1157 brake/turn/parking light. They have dual filaments; the brake side is 27W, the parking light side is 8W.
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,906
I have a auto lamp that is half burned out. Far as I know sealed SLA batteries used in UPS's are gel cell. Am I behind the tech curve on this?
 

SgtWookie

Joined Jul 17, 2007
22,210
I have a auto lamp that is half burned out. Far as I know sealed SLA batteries used in UPS's are gel cell. Am I behind the tech curve on this?
It kind of depends on how long ago the batteries were purchased.

AGM batteries have been out on the market for awhile.

If you aren't sure, then why not post the manufacturer and part number of the batteries you have?
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,906
One is a UB1280ZH
NON-SPILLABLE BATTERY
SEALED LEAD-ACID BATTERY
1280 12V 8Ah

Basically a standard in a lot of UPSs.
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,906
OK, so how does this make a difference? The batteries are pretty common, as in I can buy new from quite a few different sources, so AGM isn't that rare (did you mean Gel?). Looking them up in Wikipedia there isn't much difference I can spot.

Remember, I only want a quick and dirty test. Last time I took a battery to a local high tech battery store they broke out a test, and got a reading in 15 seconds.

I'm thinking I want to read the resistance of the battery.
 

SgtWookie

Joined Jul 17, 2007
22,210
The AGMs are much better than gel cells. You can charge them much more quickly, and discharge them more quickly, than the old gel cells without worrying about if they will develop gas pockets.

Some say you can charge the AGM's as quickly as C/3, but I'd charge them more slowly than that.
 

debe

Joined Sep 21, 2010
1,142
Hi Bill. I use several SLA batterys & they do require looking after in regard to charging & not leting them go flat as being left flat is a sure way to kill them as is over charging them. Pics of a 7.2Ah batery & its voltages for cycling & standby use. Also a spesific auto charger that charges then goes in to float charge. Best way to check a battery is charge it up & run a known load & time it for its capacity that is left in the battery. 10V is a very flat battery. Use a voltage regulated charger with these types of batterys, if you want long life out of them.
 

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THE_RB

Joined Feb 11, 2008
5,438
I charge mine on a regulated bench PSU that has a voltmeter and ammeter. If they are good and at (say) 12.4v if you connect them to 13.2v regulated they will immediately draw a decent current, maybe an amp (or about 15% to 20% of C).

If you connect it to 13.2v and the immediate charge current is low, the battery is crapped (high impedance).

Common faults are an open cell; that will immediately jump to 13.2v with no current. Or a shorted cell, that battery will read very low voltage (like 9v or 10v) and draw current on the charger but will top out at 11 point something volts and quickly drop back to 10 or so volts when charger is removed.
 

Yako

Joined Nov 24, 2011
245
If you have ever done a unit of study such as software analysis and engineering, then you would know that there first has to be a business need.

Why would we engineer a system to test batteries when very cheap products already exist, and it can also be reasonably assumed that the battery is go or no go by relying on fundamentals such as if it doesn't draw adequate current then it is likely in an high Z (impedance state)
 

SgtWookie

Joined Jul 17, 2007
22,210
If we simply ran out and bought everything we needed, there wouldn't be much point in these forums, now would there? ;)

It frequently is not affordable or desirable to just run out and buy something, when one has accumulated as many parts and equipment as someone like Bill.

He undoubtedly has all the parts & equipment right there to build just about anything he might need (if he did need to build something) - and he really likes to tinker anyway.
 

nsaspook

Joined Aug 27, 2009
6,491
That's actually not quite true. A load must be placed on the battery to properly test it.

This goes for any battery.
A common failure mode is a shorted separator in a cell from sulfate crystal growth during discharge if the battery has been sitting for a long time without being recharged. It's never going to read 12vdc rest voltage if this happens. If it's 10 volts or less with all good cells the battery life has been permanently reduced.
 

Yako

Joined Nov 24, 2011
245
A common failure mode is a shorted separator in a cell from sulfate crystal growth during discharge if the battery has been sitting for a long time without being recharged. It's never going to read 12vdc rest voltage if this happens. If it's 10 volts or less with all good cells the battery life has been permanently reduced.
I fail to see what that has to do with a textbook-referenced claim that a load must be placed on the battery in order to properly test it.

I am not just an electronics geek with trade-level qualifications -- I also like working on cars. I have rebuilt two and completely demolished another two with an angle grinder all by myself. Moreover, my battery is stuffed at the moment. It won't crank my engine at all, but the floating voltage on it implies that it is ok. When you crank you are placing a load on the battery. Not sure what it drops down to, but I am not happy because I only got 2-years of use from it and I paid good money for it too.

I have to admit that the vehicle is a turbocharged performance machine (gets very hot under that bonnet) -- but two-years for a battery costing 140-dollars? Not a happy chap.

No car projects allowed? Can't you put in a disclaimer?

I have some real good ones to offer.
 
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