Can a flat AGM battery be restored?

Submitted: Saturday, Apr 17, 2010 at 20:40
ThreadID: 77789 Views:5799 Replies:2 FollowUps:1
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Have an AGM in car that hasn't been used for 6 weeks, and is flat.
0v, well 0.3 volts.

Battery charger (Ctek) won't recognise it and try and charge it.

Hooked it up to a small battery for a couple of minutes, and got it to 7v.

Ctek will now charge it.

Have I a hopeless case, or will it come back up?

Found the 0.5 amp current draw and isolated it now :o)

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Reply By: Battery Value Pty Ltd - Saturday, Apr 17, 2010 at 21:19

Saturday, Apr 17, 2010 at 21:19
Hello Oldplodder,

the following might help:

try to put it on elevated float charging voltage for a couple of days (13.8 to 13.9V).
If you're lucky it's only sulphated up a little which should be reversible to some degree.
Observe the battery temperature. If it gets warm to the touch, reduce the float voltage to 13.6V.

After the two days on float charge give it a very shallow discharge and observe the voltage. If it holds above 12V, you've been lucky. Do a full boost charge cycle, followed by another shallow discharge and see if the voltage holds better. If yes, keep doing this until your satisfied with the result (or until there are no more improvements in the voltage under load).
At the end do a full boost charge cycle before putting the battery back into service.
Pity the cteks only go to 14.4V in boost. You want to have full boost voltage of 14.7 to 14.8V especially in such a situation (this is like a mini equalization charge, similar to what you do to flooded cell batteries every now and then).
Best of luck.
BTW, if you can't revive your AGM battery just let me know and I'll tell you where you get real Battery Value for your money ;)

Best regards, Peter
AnswerID: 413325

Follow Up By: Member - Oldplodder (QLD) - Saturday, Apr 17, 2010 at 21:33

Saturday, Apr 17, 2010 at 21:33
Thanks Peter,

It is on low ampage high voltage charge at the moment.
Will see how it is in the morning.
Have another charger which I might try later as you suggest.

It is a 30 a/h battery so shouldn't take too long to come up.

FollowupID: 683428

Reply By: Member - Phil G (SA) - Sunday, Apr 18, 2010 at 08:13

Sunday, Apr 18, 2010 at 08:13
Best of luck. A friend did exactly the same with a wetcell battery some years back - it took us a week to fully charge it. Some CTek chargers (like my XS7000) have a choice of 14.4 or 14.7 - use the higher setting, and leave it hooked up.

Last wetcell battery I had to this to, took a charge nicely, but I eventually dumped it because it was self-discharging at a great rate. I have no experience with recharging dead AGMs.

PS, you can't deliver a "low current" at a "high voltage" unless your battery is stuffed!
AnswerID: 413358

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