Battery Query


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May 7, 2023
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Hi All

Looking for a bit of advice on replacement battery.
I've got an A4 B8 Avant 1.8 TFSI (2010), had the car around 7 years, post-lockdown every now and then get warnings about low battery (getting more frequent), do lots of short journeys with the occasional long journey. Have charged a few times but same issues after a little while. Battery is showing below 12v (11.9v) when off.

Looking through past posts I was thinking of purchasing this battery

F18 Varta Silver Dynamic Car Battery 85Ah (585200080) (110)

However after taking out all the surrounding covers from the battery I think my battery is a different type?
It says AGM which I think is for Stop/Start cars, I don't have that but from a google search these are good for short journeys?
I don't have access to VCDS so was hoping to just replace like for like to save on coding.



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My February 2011 S4 has had an AGM battery from factory, and does not have Stop/Start, but probably like your car has "regenerative braking" - this means that the charging system will try to add charge into the battery unless it absolutely has to to keep the battery charged enough to start the car if it is stopped.

So, the plan is to maintain the battery at roughly 70>85% charged, in doing that it normally leaves enough "charging space/capacity" for the car to turn wasted energy on the over run and braking, into extra charge in the battery - as long as there is enough "charge space/capacity" to take in that extra charge.

As you have said, AGM batteries tolerate being left partially charged some of the time a lot more than normal wet lead acid batteries and even EFBs.

So yes, I'd suggest fitting the correct sized AGM into that car, it has been said that while initially the charging profile will not exactly fit that new battery's wants/needs, the charging parameters will adapt with time - as they did while that battery was running out of good health from new.

The question is, does anyone have documented evidence that leaving "as is" cost you more money in further battery life of this new battery and/or extra fuel on not having the charging system "not optimised" - I can't answer that question, but I will say, that I have always "logged" this battery change with cars that I have replaced the battery in - where that was recommended by VW Group.

Can't you search out a VCDS owner local to you to sort this out for a small charge/cost?
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Maybe check the rating of your current AGM, in terms of amp hours and cold cranking current, though both on the replacement will be slightly higher. Check the length, width, height and positions of + and - on your one, then head off to the Varta website and find the model/code of AGM that fits the bill, then head to Tayna and find that one and order it that way instead of letting their battery selector do that job.
Varta or maybe even JCB make Bosch car batteries, it was a Bosch one that I bought, mainly, because we are Costco members and while the Bosch from Costco near me was a few pennies more than the Varta from Tayna delivered to my door step, Costco had a "VAT free" event, so I just grabbed one then.
Yes AGM is good for short journeys.
Since you have the low battery warning the battery management system will have switched to a maintenance mode which may not be suitable for a brand new battery.
Because of this you should code the new battery. If you are doing the coding then you will be able to change the battery capacity if necessary.

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