AGM Batteries - Impressive

Mr Tidy

Mr Tidy

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 North West Surrey
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The battery in my car died in April 2021 and I had read a thread on here suggesting AGM batteries were possibly better than wet ones for cars that didn't get frequent use. (I did have a bookmark for it but lost that after the forum upgrade). Anyway based on that I bought an Exide AGM (70Ah) from Tayna.

I knew I hadn't used my Z4 this year so as it was finally dry yesterday the roads were clear of salt and I needed to go out I thought it was time to use it, and although it cranked a bit slower than usual it fired up quick enough so that was a relief. :p

When I got home I worked out I hadn't actually used it since 7 December, so it had held charge for more than 5 weeks. So I was pretty impressed!
 
Nice, no trickle charging either? So an E85/6 normally has a wet battery? That may need topping up? Mines always garaged on a CTEK.
This prompted me to look up what an amg battery actually was, as I’d never thought about it before. Interesting…
I’m sure mine will not be original. I wonder what type it is.

An AGM battery means
Absorbent Glass Mat, a type of advanced lead-acid battery where the electrolyte (acid) is held in sealed fiberglass mats between the plates, making it maintenance-free, spill-proof, vibration-resistant, and ideal for high-demand systems like modern vehicleswith start-stop technology.
 
A good battery, of any type, should hold it's charge for five weeks Iain, even in Winter.

My daughter's Polo has a cheap old normal lead acid battery in it (don't know how old it is). She has been at home for 5 weeks, uses her car once a week to go 1/2 mile and back (so it loses more charge starting it than it gains by driving it). It has no issues whatsoever.

AGMs only give the battery more storage capacity for a given physical size. They are still lead acid. Same technology, just in a slightly different way.
 
RMB said:
An AGM battery means
Absorbent Glass Mat,
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Indeed. Not re-inventing the wheel, just they provide more surface area for a given space, so can hold more electrickery. :)
 
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And, ironically, the wife's one year old Focus had a new battery (Ford OEM) fitted under warranty this week as it has been shite since the day we picked it up.
That was purely down to the car being stored at the dealership for months and them not ever charging the battery. So the battery was killed by being allowed to run down too much. Then they charged it when we bought it and thought (or probably didn't think at all) all would be good. The battery was damaged from day one and never took a proper charge again. Luckily Ford replaced it without question.
 
Pondrew said:
A good battery, of any type, should hold it's charge for five weeks Iain, even in Winter.

My daughter's Polo has a cheap old normal lead acid battery in it (don't know how old it is). She has been at home for 5 weeks, uses her car once a week to go 1/2 mile and back (so it loses more charge starting it than it gains by driving it). It has no issues whatsoever.
Click to expand...
Reading that brings back memories of my first car, a MK2 Cortina with a dynamo that couldn't always hold charge for a night out, so I always tried to park it facing downhill!
 
Mr Tidy said:
Reading that brings back memories of my first car, a MK2 Cortina with a dynamo that couldn't always hold charge for a night out, so I always tried to park it facing downhill!
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The weird thing is Iain that I have owned and driven cars for over 40 years and only bought a battery charger since I have frequented car forums! I now own two!
I have NEVER had a flat battery on a car, ever, in those forty plus years.

What does that suggest? Car forums are good at scaremongering? Or that BMWs are shite? Or I have become paranoid because of one or both? :unsure:
 
TBF I've only ever had a flat battery on two other cars that I had after that Cortina as they all had alternators.

First exception was a Mercedes C280 I bought in 1999. 2 weeks on holiday in the summer and it needed a jump start from Mrs Tidy's Micra! But it did it every year so there must have been some parasitic drain I never discovered before I moved it on.

Then my current Z4 in 2021. The battery was obviously old and tired so putting it on SORN for a month turned out to be more than it could take. :(

I think the answer is forum scaremongering or paranoia Andy. I've had 7 other BMWs with no issues!
 
I think it’s more a question of modern cars taking more out of a battery while inert. In the case of your old Cortina (or in my case my Talbot Samba) it has a reputable lead acid battery and it can stand there a lot without problem because there is no drain on it when the car is switched off. My understanding is that cars have been progressively more alive even when switched off and the batteries can go flat quite quickly. That said I have a AGM in our Fiat and it’s never charged and it routinely sits on the drive for weeks when we are in Spain. It’s fine - the first battery did die overnight though at eight yeas old last year. In winter of course. On a Sunday. When I wasn’t at home. When I needed to get somewhere!
 
In a car designed to use a normal flooded cell battery there’s no real advantage to an AGM..plus the charging regime for AGM is slightly different meaning you’re not optimising battery charging…and… AGM batteries don’t like hot engine bays…so they are placed elsewhere or have thermal insulation if in the bay..
 
B21 said:
In a car designed to use a normal flooded cell battery there’s no real advantage to an AGM..plus the charging regime for AGM is slightly different meaning you’re not optimising battery charging…and… AGM batteries don’t like hot engine bays…so they are placed elsewhere or have thermal insulation if in the bay..
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That's interesting, although it must have been pretty well charged when I parked it in December if it still worked over 5 weeks later.

Anyway there's no heat issue in a Z4 as the battery is in the boot, like all my other BMWs!
 
We just had to change the AGM battery in my wife’s 240i - original, 2016, constructed charging for the last 3yrs. Pretty impressive.
 
That is good going!

The AGM battery in my 2007 123d with stop/start didn't make it to 5 years. :(
 
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