Misleading AGM battery.
 

Charger tells me AGM battery is charged to the fullest where the charger employs auto stop...
Installed the AGM battery and it can't crank the X, not even a whine.
Battery is old last time I used it I depleted it...put it on the charger several times over the last year.
Ah ! It's cooked.

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For starters, many chargers won't charge a dead battery. You need at least to do some voltage measurements before you can tell anything.

It's possible with auto charger and very dead battery it will think it's 6v and charge to that level. Definitely need to measure the voltage.

If a battery is badly sulfated, it can also charge to full voltage but have no capacity. (that tends to be the MO of my battery deaths)

What type of charger is it? Is it a Battery Tender type? Or old fashion style?

I have used only one AGM battery, a 2012 Optima Yellowtop, in my home-built 4x8 camping trailer. It went dead in 2015? after the trickle charger died over the winter, and I didn't check it for months.

I was able to revive it using a high powered battery charger, to shock it, and a 15amp smart charger to desulfate it, alternatively over two days.

When it was dead, I had to connect a jump box to fool the high powered wheel charger into starting up, then it didn't require the chargers to be "fooled" to activate.

I have a newer charger maintainer/power supply (Clore Automotive PL2320), that will activate and charge a dead battery with the press of a button, and can also desulfate the cells.

Since that AGM went bad, I started using only smart chargers on my vehicles, 24/7/365, at home, and check them every day or two. Maybe you can revive your AGM. My 2012 AGM is still good even today.

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Smart charger...
It can auto select AGM or standard.
And has auto shut off.
It can charge at various levels as the battery becomes fully charged. Got it off Amazon couple years ago.
Portable light weight about the size of a cigar box...from China I suppose.
Today I intend to drop it off at Auto Zone ....get feedback then.
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Picked up the battery from AZ... battery dead! After a day's worth of charging.
I'll use as to cover core charge in the future.

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The smart charger I used back in 2015, to save the AGM battery (along with the wheeled heavy-duty unsmart charger), is also very lightweight. It's a Schumacher XCS15, and it's probably 15 years old now, and it's in the trunk of the X5, just in case. But, my new favorite, the Clore Automotive PL2320, is a bit more substantial, has added features, and I use it as my primary charger, now. I still use the 30 year old wheeled charger, only if I'm needing to jumpstart a nearly dead battery, fast.

The old rule of thumb was that "the heavier your charger is, the more durable it is". Perhaps so, but the solid state chargers are getting better all the time.

Agreed

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