RecoverE
Posts: 27
Joined: Tue Jan 09, 2018 8:06 am
Location: Upstate New York

12V Battery Replacement Questions

Fri Sep 18, 2020 11:17 am

I am into my sixth year with my 2015 eGolf @44Kmiles and want to replace my 12V Varta AGM battery with a Duracell AGM. They both have the same form factor including the mount holes for the terminal covers. The Varta is a 58Ah unit and the Duracell is 60Ah.

I plan to maintain voltage in the system during the exchange via a third battery appropriately connected via terminal clips. Can I expect a clean swap without the need for a service visit to register the new battery to the car? If there is a mis-registration with the new battery, what are the consequences until the issue is corrected? Is the car still usable?

I want to take this action now to see if a fresh battery (higher terminal voltage) will help with my occasional charge fault issues; i.e., failure of the power plug locking pin extending/retracting. So, I would appreciate any comments.

Thank you

Spektre
Posts: 136
Joined: Mon Jun 13, 2016 8:14 am

Re: 12V Battery Replacement Questions

Sat Sep 19, 2020 6:28 am

YMMV, but in my experience, replacing the 12v battery requires coding at the dealership (or DIY if you have OBDeleven or equivalent.)

I experienced the same disturbing behavior - bucking, error messages, etc - after replacing the battery as I did before removing the bad battery. Once I had it towed to the dealer, they coded the new battery in the system and it's been fine ever since.

I was able to find quite a bit of relevant info with this search.
Hers: 2021 Tesla X Long Range Plus
His: 2015 eGolf SEL Premium
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RecoverE
Posts: 27
Joined: Tue Jan 09, 2018 8:06 am
Location: Upstate New York

Re: 12V Battery Replacement Questions

Sat Sep 19, 2020 8:22 am

Spektra, thanks for your response. When replacing your battery, did you maintain 12V battery voltage on the system when swapping batteries?
I am really torn on doing this exchange now given no obvious low voltage issues. However, my local VW dealer has little eGolf experience, so this fact is concerning also. In the absence of any additional encouraging comments, I probably will wait until I need dealer service for break/cooling system fluid replacements.

Thanks again.

f1geek
Posts: 851
Joined: Fri Jan 23, 2015 1:18 pm
Location: SF Bay Area

Re: 12V Battery Replacement Questions

Sat Sep 19, 2020 12:44 pm

I believe coding is an absolute requirement so the car computer knows you installed a new battery. Not coding will probably lead to continued problems. I imagine the coding for an e-Golf is identical for an ICE Golf for a new 12 V battery.
2017 e-Golf LE, Multi Coat White with Black Vegan Leather interior

somethingcool
Posts: 28
Joined: Mon Jun 01, 2020 4:40 pm

Re: 12V Battery Replacement Questions

Sat Sep 19, 2020 2:41 pm

Uh, definitely YMMV. I've had the 12v disconnected for more than a few hours on multiple 2019 eGolfs without issue. Sometimes you get the Christmas lights on startup but a turning it off and on a few times and a drive around the block always returns everything to normal in my experience. Maybe it varies per year, but I think you are reading way too much into a few people that had issues, the car was not designed to need "coding" for a 12v battery swap, not sure what that even means? The car has no way to tell one 12v battery from another.

What seems more likely to me is codes got thrown on cars that were running with bad 12v batteries, putting out low/unclean voltage and causing issues unrelated to the swap. Which would indicate your plan to swap before issues arise is a good one.

I would also not recommend this third battery to maintain voltage idea, seems way too likely to cause issues if you don't know what you're doing. Just swap one for one, no need to maintain connection at all times.

RecoverE
Posts: 27
Joined: Tue Jan 09, 2018 8:06 am
Location: Upstate New York

Re: 12V Battery Replacement Questions

Sat Sep 19, 2020 3:05 pm

Thank you gentlemen for your comments. I did not realize that VW Golf MK7 ICE models had coding info. Interesting reading for me. Given the negative terminal current shunt, it seems that there is an effort to optimize charging as the battery ages. I will continue my research and again welcome further comments. I suspect that if I replace the OEM battery with one with similar specs, no coding will be necessary.

Spektre
Posts: 136
Joined: Mon Jun 13, 2016 8:14 am

Re: 12V Battery Replacement Questions

Sun Sep 20, 2020 6:54 am

somethingcool wrote:
Sat Sep 19, 2020 2:41 pm
Uh, definitely YMMV. I've had the 12v disconnected for more than a few hours on multiple 2019 eGolfs without issue. Sometimes you get the Christmas lights on startup but a turning it off and on a few times and a drive around the block always returns everything to normal in my experience. Maybe it varies per year, but I think you are reading way too much into a few people that had issues, the car was not designed to need "coding" for a 12v battery swap, not sure what that even means? The car has no way to tell one 12v battery from another.
Disconnecting the same battery and replacing the battery are two very different things. No one is reading anything into this, it is fact. There are 4 fields in VCDS that must be updated when replacing the battery, especially if it varies from the specs of the one you are replacing. At the very least the serial number field must be changed to let the car know it is a new battery.

https://www.golfmk7.com/forums/index.ph ... lf.320084/
Hers: 2021 Tesla X Long Range Plus
His: 2015 eGolf SEL Premium
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f1geek
Posts: 851
Joined: Fri Jan 23, 2015 1:18 pm
Location: SF Bay Area

Re: 12V Battery Replacement Questions

Sun Sep 20, 2020 2:55 pm

Some more information:

http://wiki.ross-tech.com/wiki/index.ph ... eplacement

and

https://www.youtube.com/watch?v=IJAScg6JrYI

At least you need to let the 12 V battery management computer know you installed a new battery and let it know Ah of said battery. It is most certainly easier to do nothing but swap the battery. If you've already spent money on a new battery, why would you not want to let the computer know you've done this so that the new battery is charged correctly?
2017 e-Golf LE, Multi Coat White with Black Vegan Leather interior

somethingcool
Posts: 28
Joined: Mon Jun 01, 2020 4:40 pm

Re: 12V Battery Replacement Questions

Thu Sep 24, 2020 9:19 am

f1geek wrote:
Sun Sep 20, 2020 2:55 pm
If you've already spent money on a new battery, why would you not want to let the computer know you've done this so that the new battery is charged correctly?
Because the eGolf does not have a BEM system requiring this coding change. It's specifically for vehicles with stop/start systems. It won't hurt anything, but it also doesn't do anything, waste of time and effort.

Even for vehicles with start/stop/BEM not coding is fine, the ECU adapts to the new battery with time, making this coding useful but not required.

somethingcool
Posts: 28
Joined: Mon Jun 01, 2020 4:40 pm

Re: 12V Battery Replacement Questions

Thu Sep 24, 2020 9:23 am

Spektre wrote:
Sun Sep 20, 2020 6:54 am

Disconnecting the same battery and replacing the battery are two very different things.
No, they are the exact same thing. This coding is for BEM equipped cars with start/stop feature. Does nothing in the egolf and is not even required in BEM equipped cars. You are misapplying information here without understanding the context.

The link you provided even acknowledges this: "Any VAG “MQB” platform cars (not Hybrids or Electrics)."

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