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Old 03-30-2007, 10:25 PM   #1
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Battery question -- won't take charge

I picked up some used deep cycle 12 V gel cell batteries for Millicent. One of them won't
take a charge. It shows about 11.5 V on a volt meter, but when I put the charger
on it, the Amp meter barely twitches. The others suck it up at 5 to 10 Amps.
I suppose it's "toast"?
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Old 03-30-2007, 10:38 PM   #2
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That would be my guess, but heres the thing....are they actually gelled electrolyte batteries or are they actually absorbed glass mat sealed lead acids?

The charging algorithm is far different for the two chemistries. An AGM can be charged in roughly the same was as a VRLA or a wet lead acid battery. They differ slightly (they actually are more forgiving when it comes to high charge rates), but will charge roughly the same way. They are well suited to a relatively low amp draw over a long period of time.

A gel battery, on the other hand, requires a very specific charging system. It will bulk charge up to 90% very quickly, but that last 10% will take a long time and will require a specific charger. The gel is better suited to high amperage intermittent use like that that would be seen in an electric wheelchair where it is starting and stopping all the time with high draw motors, but needs to last all day and be able to take a deep depth of discharge.

Deltran makes automatic chargers for both types of batteries. Other companies do as well, but I really like the Deltran line. Unfortunately you pay for the name.

My guess is that that battery is gone if your charger worked on the others. Check the surface charge on the others after they have say atleast overnight. As a general rule 12.6v is a full charge while 11.8 is totally dicharged. Anything below that is damaging and in reality we like to see them stay above 12.2 volts in a business that deals with warranties. You mileage will vary.

I would try a different charger if you have one and see what happens. Manual chargers are generally more able to cope with deeply discharged or damaged batteries.
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Old 03-31-2007, 12:08 AM   #3
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I'm pretty sure I read the word "gel" on at least one of them. They are back-up
batteries for cable TV systems. They live in a box up on a telephone pole for a
couple of years, and then are replaced.

I achieved a 12V surface charge on this iffy battery after trying the charger
for a short time, but the volt meter was enough to draw that back down towards
11.5 while I watched. So 11.8 is pretty much it, eh.... I guess that answers
my question! One dud out of twenty ain't bad. Specially when they were free.

I did get a charger for them also. It charges three of them at the time, in series.
There are indicator lights showing the current (sorry ) mode of charging.

And on one of the batteries I saw charging specs -- different voltages for... I'll
have to read up on it again.

Thanks! I wanted a second opinion before I recycle it.
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Old 03-31-2007, 01:38 AM   #4
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That voltage is key. That's where the different charging algorithm comes into play. A wet lead acid battery, VRLA, or AGM will have three main charging stages...bulk where the voltage rises, but the amperage is pounding, absorbation where the voltage is held constant with trickling off current, and then the float charge which just keeps it charged up. A gel is totally different in how it is charged, but generic specs aren't all that important. Just follow whatever the manufacturer has stamped on it. I'd go by the lowest rate given that it is easiest on the battery and you probably have nothing but time at the moment.
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Old 03-31-2007, 01:45 AM   #5
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Oh yeah....one more thing....cook that old battery. If it's bad you aren't going to lose anything, but you wouldn't believe the number of batteries we've brought back at work just by really charging them. People get really afraid of overcharging and end up putting a trickle charger on a big Group 27 deep cycle for 12 hours and wonder why it won't come back. We put it on a 40 amp charge for 90 minutes followed by an absorbsion charge and amazingly they will test out like new on a carbon pile load tester.
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Old 03-31-2007, 02:00 AM   #6
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Some of this info is too technical for me. But since I have the fancy charger that
goes with the batteries, I'll just hook'm up after use.

What about right now? I don't know how long the batteries have been out of service,
and it may vary, but it should be mostly just a few weeks. Should I hook up the
36 V charger, or is it good enough to rotate a "battery tender" among them
to keep them healthy?

Try 40 Amps on that problem child, eh? My old regular K-Mart automotive charger
is only good for 15 Amps.

Let's get some shut-eye, guys. Zzzzzzz
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Old 03-31-2007, 02:23 AM   #7
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Sleep is for wimps.

I wouldn't put 40 amps to those batteries necessarily. Heck, I don't even know what size they are. I could help you decode them, but that's neither here nor there.

A Battery Tender is AWESOME as long as the battery is already charged or mostly charged when you put it on there. A Battery Tender is one of those chargers that doesn't take well to deeply discharged batteries because of the microchip controlling it.

How big are these things? Do they give an amp hour rating? Follow their charging directions, but on that bad one it might not hurt to leave it on a little longer if you have the time.

That 36 volt charger will bulk charge those babies just fine. If they're wired in series you do run into one problem in that you could have a completely dead battery in the group but the other two will compensate. I've seen it confuse a few computers in chargers, but even Deltran says it's just fine to parallel batteries on a Battery Tender. I don't see why running in series would hurt too much as long as the batteries were somewhat matched in surface charge when you start.

People have as many opinions about batteries as they do politicians so we don't need to get much more into it than we already have. Just do as you're doing. Even if half of those batteries turn out bad you still got 10 free gel cells! I work at a battery store and the best I've ever scored is a Group 75 battery that failed at it's rated output, but worked just fine for starting a Honda after some cutting, hammering, and wiring adapting. Some guys just have all the luck!
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