2015 Passat TDi Battery Swap

c3kTDi

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2015 Passat
Yeah, I know: another battery swap thread. But, this time it's different. This time it's about my car. ;)

(FWIW, I did a search "battery swap" in this forum and got a page and a quarter of hits. They're all over the place. Some had Golf gassers, some were changing the SIZE of the battery, etc. I couldn't find a definitive swap guide.)

I've got a 2015 Passat TDi. Yes, a diesel. I'd like to keep non-diesel comments out of here.

The original battery is still in it, but I've been getting some long cranks if the car's been sitting for a few days. The most recent was a day ago. I parked at the airport from Friday the 13th through early Tuesday morning, the 17th. Daytime temps were in the 90s, nighttime low 70s. When I got in, it cranked at a normal speed for about 7-8 seconds before the engine started. This crank time is getting longer and longer. If I shut down and restart, it'll fire right up.

I'd considered the VVT valve leak (great thread), but thought I'd hit the battery first.

After leaving the vehicle shutdown and parked for a day and a half after driving it home for 90 minutes of highway driving, my battery tester (Foxwell BT100) showed SOH at 87% and SOC at 59%. (12.29v <- I think. That was a few hours ago.) and a "Battery Recharge" message, indicating it just needs to be charged.

I think the SOH of 87% is false. It should not have dropped to such a low voltage. And, almost 80k miles and living in the South with plenty of multi-day sits in the outdoors.

I'm going to buy a new battery to hopefully fix the long cranking.

OEM is 5K0 915105G and shows 72Ah and a (paltry) CCA of 380 (CA may be 640 from what I interpret on the label). I think it's a basic lead-acid battery.

I want to swap in something a bit...hardier. I'm looking at some of the AGM style, BCI size H6 (or Size 48). For one of them, it shows 760 CCA and 875 CA, with a reserve of 120 minutes. (I'm not sure what that means for Ah rating.)

Now, I know it CAN provide more amperage, but that doesn't mean it's gonna flip the starter out of the car. I want more reserve.

I've got Ross-Tech's VCDS. What an outstanding, if difficult to understand, tool. Their support eases any issues with figuring it out.

If I put the new AGM battery into my Passat TDi, will I need to reprogram the BCM or BEM? (Do I even have a Battery Control Module??? Does the Body Control Module care about the battery type?)

I'm aware of the THEORETICAL differences between lead-acid and AGM recharging. I don't want to hear it. :) Does the Passat accept programing to change the TYPE and SPECS of the battery?

Thanks!

Ken

TL;DR: what do I do to swap in an AGM battery into my diesel?
 

thundershorts

Top Post Dawg
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west chester pa
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2015 passat tdi sel premium 2015 golf s tdi gls tdi b5.5, 2002 eurovan,Peugeot 505 td,Citroen cx25 prestige
Bought and installed new battery yesterday, replacing original enertec with a Varta from VW. 75k miles, 5 yrs is really good for a battery. The vw/Varta was 40 less than other choices and marked made in germany, built 7/21. Why not just use the Varta?It probably will last just as long,5/yrs which equates to less than 25/yr.
 

oilhammer

Certified Volkswagen Nut & Vendor
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outside St Louis (where it's safe)
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There are just too many to list....
We only use the OEM type batteries from the dealer in VAG products anymore. They are reasonably priced, fit correctly, last a long time, and anymore all the aftermarket brands have such spotty quality it just isn't worth the hassle to try anything else.

And no, your 2015 NMS Passat does not have a battery regulation module nor is there one coded into one of the other modules. An AGM won't do a darn thing for your car.

And your long crank time has nothing to do with your battery, either. In fact, that problem is actually displaying that your existing battery is in good health.
 

c3kTDi

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Feb 3, 2019
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2015 Passat
We only use the OEM type batteries from the dealer in VAG products anymore. They are reasonably priced, fit correctly, last a long time, and anymore all the aftermarket brands have such spotty quality it just isn't worth the hassle to try anything else.

And no, your 2015 NMS Passat does not have a battery regulation module nor is there one coded into one of the other modules. An AGM won't do a darn thing for your car.

And your long crank time has nothing to do with your battery, either. In fact, that problem is actually displaying that your existing battery is in good health.
Well, with a 6+ year old battery and a new issue of long cranks before ignition, where else should I start troubleshooting?

(And since I park my car for extended periods at the airport, what HARM will a deeper battery do?)

Ken
 

thundershorts

Top Post Dawg
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Location
west chester pa
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2015 passat tdi sel premium 2015 golf s tdi gls tdi b5.5, 2002 eurovan,Peugeot 505 td,Citroen cx25 prestige
Your car charging system was designed for a lead acid standard battery, which has functioned fine up to now. A new Varta/vw battery should last just as long for you, why reinvent something that isn't broken? Your long cranking is probably caused by low voltage to the ecu during starter engagement. New battery will cure this.
 

thundershorts

Top Post Dawg
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Location
west chester pa
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2015 passat tdi sel premium 2015 golf s tdi gls tdi b5.5, 2002 eurovan,Peugeot 505 td,Citroen cx25 prestige
Battery replacement is easy as long as it fits correctly, Hold down lips are correctly made, etc. I think the Audi a3 tdi 2015 had start-stop so it would have had a agm. You could get an Audi/Varta agm h6
 

740GLE

Top Post Dawg
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NH
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2015 Passat SEL, 2017 Alltrack SE; BB 2010 Sedan Man; 2012 Passat,
FYI audi a3 is based of the mk7, not the NMS.

So same could be said for mk7 being able to properly run an AGM, but alas NMS doesn't have all the BCM upgrades of a MK7.
 

Jetta_Pilot

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West Hill, Ont. Nov.2nd in Mexico till April 27th
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2015 Passat Highline TDI Candy White (SEL Premium) long gone 2002 Jetta TDI
I changed to a larger physical size 8H Duralast AGM battery. Took a bit of work to make it fit since the AGM is about 3" longer. I had to totally remove the battery tray and modify it to fit since the tray has certain things on it which will not allow a non VAG type battery to sit flat. In my VCDS there is a setting I changed from FLOODED battery to AGM battery. To the best of my knowledge an AGM battery wants a lower charge rate compared to a flooded battery. My car may sit for weeks and the AGM battery has never let me down.

Also see more info here:
 

c3kTDi

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2015 Passat
Well... I did it: I used an AGM (with twice the CCA rating, 760CCA) to replace the OEM.

After hooking up VCDS by Ross-Tech and being thoroughly confused, I contacted their Customer Service to get some instructions on modifying my BCM to adjust for the AGM.

Wasn't I surprised when they advised me, after sending them some files, that my 2015 VW Passat TDi does NOT HAVE a BCM. Call that sorted...

Now, with the new battery, the engine fires right up. Color me happy.
 

Jetta_Pilot

Top Post Dawg
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2015 Passat Highline TDI Candy White (SEL Premium) long gone 2002 Jetta TDI
See my post above !


In my VCDS there is a setting I changed from FLOODED battery to AGM battery. To the best of my knowledge an AGM battery wants a lower charge rate compared to a flooded battery.
 

c3kTDi

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2015 Passat
See my post above !


In my VCDS there is a setting I changed from FLOODED battery to AGM battery. To the best of my knowledge an AGM battery wants a lower charge rate compared to a flooded battery.
Yeah, the AGM has a lower internal resistance than a flooded battery, but when your alternator is "dumb", well, it'll just let the juice flow until the AGM meets the same voltage level. I've yet to see a lessened AGM life due to this... I'm going with it.

(And, my VCDS had no setting for that change, since I have no BCM.)

Thanks!
 

c3kTDi

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c3kTDi

(And, my VCDS had no setting for that change, since I have no BCM.)

Well that setting doesn't just stare you in the face. You'll need to look for it !!!
Seriously...thanks for looking out for me.

When I used VCDS, I dove right into Module 61. It =seemed= to be there, but the dropdown menus didn't work. Then I went into the Module 19 (body?). I saw some stuff, but again, it was "off". Finally, I contacted Ross-Tech. They're great. Patiently, they directed me to autoscan my vehicle...and I have NO Module 61. Nor is there any Battery Control Module (per them and me searching). My alternator feeds the battery directly.

Having studied AGM vs Flooded batteries exhaustively, I =know= that there is a theoretical loss of life to an AGM when it is treated as a Flooded (meaning charge rates). But, that loss could only be a few months, measured over a life of nearly a decade. I'll go with it. ;)
 

740GLE

Top Post Dawg
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NH
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2015 Passat SEL, 2017 Alltrack SE; BB 2010 Sedan Man; 2012 Passat,
IMO coding the battery plays a more vital role on Auto start stop as the duty cycle is way higher than those cars without. No science or data behind it but just my hunch.
 

BRIAN427COBRA

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Aug 20, 2003
Location
Sanger, Texas
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2003 Jetta, 2015 Passat SEL
I changed my 2015 in the parking lot of Oriely's, new battery was not an exact size n capacity(bigger) no coding no issues, its 2021 the stock or original battery needs to be RR(removed and replaced) NO I repeat NO coding required.
 
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