Another 12v AGM Battery


New Member
12 AGM Battery number 2. This is a different AGM battery I asked about earlier.

This is a 12v 900 cool cranking amp car battery. Convince the battery is the original battery from a 2008 car. Battery still seal never opened. Do not believe the battery was ever overcharged and was working well the two years we owned it during normal driving.

Then,... Car sat a while because of Covid will not start on it own need a boaster to start.

Will not charge fully when charged with floating charger. (it would be like charge with floater charger car would start, drive to story, and, will not then start without boaster).

So remove battery place on batter desulfater for about 2 weeks. Load test show 600 Cool Cranking Amps no self discharging (happy right).

Put in car start up right away. 2 weeks later still start but notice weak battery. Load test show 200 amps. But voltage steady at 12.4v So desulfate for another 2 weeks in car. Load test still show 200 amps.

So any idea what happen. It is not self discharging but how did it go from 200 Amps to 600 Amps and then Back to 200Amps.



Solar Enthusiast
Heh, consider yourself lucky it's even functioning at all being a circa 2008 battery! But still..

Jump starts, float chargers, aging affects, mere usage for a starter battery not designed to live longer than 4 years under normal use. Desulfators and the like.

Sorry man, we're totally in the weeds now.

Cut your losses and cut that battery loose to the recycler, and start fresh.

This is kind of the same situation I've dealt with when my buddies try to revive zombie Optima batteries and then scream about warranty and quality control. They don't like me when I give them the straight up truth that some kinds of battery use/abuse and normal wear and tear are just not recoverable.

Just being honest - your time is more valuable than this. Start fresh for both your solar and vehicular use with that batt. Anything further is just endless speculation.


Solar Addict
When a lead acid battery sits at a low state of charge, soft sulfate turns into hard sulfate crystals that desulfators cannot remove.

Pretty much end of life for the battery.


Solar Addict
If this is a car battery, take it to the AutoParts store and have them test it. That will just confirm what the others have said.

You mentioned it’s AGM, so there’s not a lot that can be done to recover it. With a FLA battery, there’s YouTube videos about high current and a little higher than normal charging voltage that will cause the cells to bubble, which is a very bad thing for AGMs, but fine for FLA batteries. This can recover some bad FLA batteries. There’s even videos about draining the acid, cleaning the cells with a solution of baking soda, and then adding the acid back in through a coffee filter.

Honestly though from other forums and from people who do this to recover FLA batteries, it works good on the batteries your dad had in his car in high school, but not so much with today’s lead acid batteries. THose who’ve tried to recover dead lead acid batteries, stop doing it. Some have said 9 out of 10 modern batteries they get are just plain dead.


Solar Enthusiast
I have to give tankace credit for being honest early on! That means I'm more likely to try and help in the future.

Unfortunately, when trying to help people figure out agm problems, they aren't up-front about the history of it.

Invariably, about 60 messages into the thread, we find:

1) I'm not the original owner.

2) It wasn't purchased new, but has already seen use in a vehicle. Or found in the garage. Or in a parking lot at the beach.

3) Homegrown attempts to "revive" it like trying to burn out the sulfate with a welder in reverse polarity. Or attaching a weedy 800ma battery tender over and over as it times out - and got so hot that they had to take it to the back yard lawn.

Only then do they hit the forums.

Most don't understand that Even-If-It-Works, sulfation EXPANDS in size, and breaks things internally. Or warps and shorts things out.

So even if the desulfators worked to have a squeaky-clean plates again, the battery is damaged by the physical expansion of the sulfate in the first place. Sadly, they'll say it ain't so, since the battery will now support a string of led lights for 4 hours. :)

Some of my buddies that aren't too battery-savvy, get the gross example of poor dental-care and tooth-plaque. Kinda goes like this:

1) You haven't brushed your teeth for years. Or not well enough.
2) When the dentist scrapes away the plaque, what does he find underneath? A cracked-tooth.

Now they understand. :)