As long as that doesn't have battery acid that sloshes around AGM doesn't leak even if it cracks open. (Had that happen to my W201 so fearful if it is liquid)...

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So it is safe to use?


Meanwhile I found few AGM used batteries with same problem when surfing Used AGM Battery and nobody says anything about concave

 

Yes AGM, SLA not sure...

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Thank you, I continue to use it because battery start car without any problem,and voltage is good...

__

So why this is happening, what I'm doing wrong? :/

I found one more example...

 

I don't think you did anything wrong. Sidewall strength of Mercedes batteries seemed suspect (to me) ever since that day mine exploded outside of church as I tried to start to head home.

The reason I'm not scared for you is because even if it does break the acid is Absorbed in a Glass Mat. No worry about acid (H2SO4) flowing around damaging things.

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Oh, I hope your w201 is ok


I'm only worry can this cause fire, explosion or something very bad to the car...
If it stopped working one day, it's ok,I will buy new, no problem

Aren't all AGM batteries vented? Mine is and it's made by Johnson Controls who owns Varta.

I think yes,my have 2 standard pipes like any other battery, but they only active when agm battery is overcharged as I know

 

Prior I tried to loyally buy Mercedes batteries and parts, after getting stuck, haven't bought a Mercedes battery since.

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Aren't all AGM batteries vented? Mine is and it's made by Johnson Controls who owns Varta.

EDIT: Never mind.................one way valve to release excessive pressure, so I guess vacuum can occur under certain situation.

 

Aren't all AGM batteries vented? Mine is and it's made by Johnson Controls who owns Varta.

Yes I believe so too and as it says Valve Regulated Lead Acid (VRLA). So any over pressure would be vented.

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I’d trade it in under warranty

 

I have no warranty


So, my final question, what is the worst thing can happen to my battery? I hope that is not a fire and explosion, anything else is ok...

 

As posted - AGM have overpressure valve, but not a vent, so they will hold some pressure.
Looks to me that having car in colder temperatures- you battery got negative pressure, what create the wall concave.
With driving, you exposed it to higher temperatures and pressure equalize.

 

I think the same too, but the picture was taken when the outside temperature is 25°C, that is not cold at all

My theory is that the battery is sometimes in history overcharged and little gas went outside, and now when conditions are normal, that "outed gas" is missing and makes vacuum

Interesting is that when the car is actively driving, only negative getting back to normal, positive for now is same

 

How long it was 25C ?
Plastics also tend to have some memory. When deformed for long time, they will stay in new shape.

 

Hmm for 2-3 days
but in March this year the battery stays the entire month out of the car, in the cold garage, but I didn't pay attention to the outside condition when I mount it back to the car

 

We have a dead Porsche battery in our possession. (I kept it because you are advised to program a battery replacement so the car charges it with a new battery profile. The Walmart AGM does not have part # nor serial # in the correct format so people reported using the old numbers and changing a digit in the SN which I did).

It has the exact same convoluted walls. I hadn't noticed! There is a Walmart bought battery in the car now. I'll check to see if it's starting to develop these when I get a chance...

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I can confirm the EverStart AGM H8 also has these convoluted walls after a few months of minimal (COVID) use but after sitting maybe a year or two on a maintainer. (It was transferred from a BMW E90 that was not being used). It's not visible but felt when running fingers along the side...

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