Four days ago, I placed a rather dead AGM battery on a CTEK 7002 battery charger. For two days the battery charger showed dead as a door nail. So, I read where one can take battery cables and jump a known good AGM battery to a dead AGM battery for one hour while the dead battery is on a charger.

Low and behold, it worked! It did, however, take another three days for the battery to come up to full charge. My question is how much longer should I leave this formerly dead AGM battery on the charger? two days? three days? or should I remove the CTEK charger now?

If the charger says it's fully charged I would remove the charger....although no harm in leaving it connected just to maintain the charge.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 157k miles
06 E320 CDI "Rutherford", Black on Tan, 175k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 70k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Battery gone dead again; I just put it back on the CTEK 7002 charger this evening. I am hoping and praying the battery recovers fully but I am having my doubts. Is there anything I can do to help the situation?

with an agm, its done. You have lost a cell. It surfaces from the charge and then fails. If it was a wet cell, you could add disolved epsom salt and put it on a hot charge.

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have no worries.....President Obama swears "If you like your gun, you can keep it

I’ve been having really good luck using a pulse reconditioning charger on my wet cell in my SD. I don’t have any experience using it on an AGM though it has a setting for AGM batteries. There is a good chance you’re dead in the water. I used those on my motorcycles and my experience is when they die they’re dead.

Not sure if these Chinese desulfator chargers are snake oil. My observations have been my six year old battery loses its ability to charge off the alternator after six months. Then I use the pulse desulfator (Nexpeak NC101). And it’s good for another six months. Then the process repeats. And I revive it another six months. I’ve done this four times over the last two years. I think given my battery style and the type of sulfate damage it is having an effect.

I’ve been driving on a six year old Everstart Max 3 year battery this way. I’ve been through many of these batteries during the last 14 years because they seem to last an average of 4 years. They kind of suck IOW but they’re cheap at Walmart. I don’t particularly abuse them and I drive the car five days a week. They just seem to die. I’ve been able to extend their life with the pulse recovery charger.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

The ctek is a great charger, and the answer to your original question is that if it's fully charged, then by all means take it off the charger. There are 7 levels on my charger, 6 is finished, and the 7th is just a maintenence level.

That all said, the charger can't rehab batteries forever. If you said it's dead again, then don't play with fire. You will depend on that battery and it will fail and leave you in a lurch somewhere. GO BUY A NEW BATTERY. Your best bet is probably Sam's Club or Costco, and maybe even Amazon, but ditch the bad battery now before you get in serious trouble on a Sunday evening when all the stores are closed and you're at the lake and the car won't start. Don't be a fool. Spend the money, get a new battery.

Oh, and use the ctek once a year on your new battery to keep it in good shape, and after any deep discharges. Like I changed my fuel filter the other day and you have to crank the battery a lot until the filter is full of fuel. That's a deep discharge.

I'm beginning to believe that it is necessary to keep an AGM battery on a charger at least 80% of the time you aren't driving. Otherwise, an AGM battery dies a slow and painful death.

Well yeah if you killed cells in your battery it is going to keep dying quickly, as others have pointed out......


Get a new battery. I have had AGM batteries for many years. The one in my w212 is 8 years old at this point and perfectly fine, never touched a charger under my ownership and I have gone 2-3 weeks without driving it.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

this is a Sam's Club Duracel AGM battery. It appears my mistake was:

A. not driving the car for a long period of time

and

B. not putting the battery on the charger during this long period of non-use.

Still, I am surprised that it has died so quickly. It is only a few years old.

I just found my Sam's Club receipt for the battery purchase; march of 2016 so it looks like the AGM battery is out of warranty.