Safe to disconnect battery (2014 Beetle TDI)?

Hello group! I drive my 2014 Beetle TDI very infrequently and it often is sitting around for three weeks, sometimes more. Is it ok for me to disconnect the battery during those periods of inactivity (to prevent parasitic drain)? I have done this a few times now and there are no issues with the keyless entry system after, which was my main concern. I do see ECU error warnings on the dash after reconnecting, but those seem to go away by itself once I drive the car (or when I clear with OBDeleven app & dongle). But I also read somewhere that there may be issues with emissions checks when the battery is disconnected, meaning that the car may fail the next DMV emissions check. Is there anything to that?

Thanks!
-J

The bug will have to be driven 50-100 miles before it will pass state inspection after the battery has been disconnected, otherwise it will not have done all of the checks to set readiness.

Why not just connect a trickle charger if you're concerned about this?

06bluebeetletdi said:

The bug will have to be driven 50-100 miles before it will pass state inspection after the battery has been disconnected, otherwise it will not have done all of the checks to set readiness.

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Thank you -- I suppose there's no way to clear anything using VAGcom or OBDeleven, right? The car has to be physically driven for that distance for the readiness checks?

Jetta_Pilot said:

Why not just connect a trickle charger if you're concerned about this?

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It's a good idea but my car is parked in a location where I have no access to a power outlet.

cannondale0815 said:

Thank you -- I suppose there's no way to clear anything using VAGcom or OBDeleven, right? The car has to be physically driven for that distance for the readiness checks?

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Correct. Driven, and run thru a variety of speeds, RPMs, etc.

It's specifically designed so you can't just clear all the codes in the parking lot of the emissions tester.

Vince Waldon said:

Correct. Driven, and run thru a variety of speeds, RPMs, etc.
It's specifically designed so you can't just clear all the codes in the parking lot of the emissions tester.

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Makes sense -- thank you!

I have cars that sit for a month+ and have no issues. The alarm will go to a low power mode after a while, on the older cars the little LED on the door will stop blinking when this happens, I think the newer ones are the same, but the car should still be fine. No reason to disconnect the battery really.

For whatever reason, our '12 Passat would always kill the battery if it sat for a week. For a while it would kill it after just a few days. Never figured out what the cause was.

I ended up leaving it on a 2a charger if it was going to sit for a while.

-J

oilhammer said:

I have cars that sit for a month+ and have no issues. The alarm will go to a low power mode after a while, on the older cars the little LED on the door will stop blinking when this happens, I think the newer ones are the same, but the car should still be fine. No reason to disconnect the battery really.

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That has always been my experience as well, but with this car, I have seen the battery die after three weeks of inactivity. I attribute it to a combination of bad battery (has since been replaced) and an aftermarket radio with always-on canbus module.

I'll see how this new battery fares and will measure the battery capacity every few days.

If the car can't go into sleep mode due to the aftermarket radio, it will use more power running the battery down faster. That seems to be your issue.

So I have gathered some more evidence related to my parasitic drain.

Through voltage-drop measurements across all fuses, I found that one particular 20 amp fuse (no. 23 in the interior fuse panel) is having a voltage drop of .6 mV between the two contact points, which, according to this voltage drop chart, translates into 187 milliAmps.

The test was performed with all door latches in the locked position, then waiting a couple of hours to ensure all systems enter sleep mode.

According to a fuse diagram I found somewhere for my car model, the fuse in question (fuse no. 23 in interior panel) serves the following purposes:

Rain/light recognition sensor -G397-
Vehicle Electrical System Control Module -J519-
Telephone Transceiver -R36-
16-pin connector -T16-, data link connector -GX22-

I checked my car for error codes using OBDeleven, and found the following faults that may be related:
- Gateway module: Telephone Transceiver (No signal/communication)
- Telephone module: Telephone microphone (open circuit); Left audio channel for speech/telephone (open circuit); Right audio channel for speech/telephone (open circuit)

These errors have been there for a while and keep coming back periodically when cleared. My mobile phone is connected via BT directly with the Android HU, so I don't need the car's telephone function anymore. But I wonder if the above Telephone related errors could be the cause of the parasitic drain somehow. Are there perhaps some coding changes I can perform to tell the car that I don't need it's Telephone function and also not the speech control stuff?

Any suggestions appreciated!

P.S.: The aftermarket radio is not the direct source of the parasitic drain -- the drain continues even when the respective fuse is completely pulled, and there is also no measurable voltage drop at that fuse

Not a direct answer to your question, but just wanted mention that your 80 A-hr (80,000 mA-hour) battery can supply that 187 mA drain for months... and months.

Meaning: it's probably not doing any harm, and likely not the main source of any issues you're having.

Could be a symptom of something else I suppose, but I would have thought you'd have found a bigger drain elsewhere.

Vince Waldon said:

Not a direct answer to your question, but just wanted mention that your 80 A-hr (80,000 mA-hour) battery can supply that 187 mA drain for months... and months.
Meaning: it's probably not doing any harm, and likely not the main source of any issues you're having.
Could be a symptom of something else I suppose, but I would have thought you'd have found a bigger drain elsewhere.

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Thank you Vince -- I've read elsewhere that a 50mA draw is considered normal, so this being more than three times that, I concluded (perhaps incorrectly) that it could be the source of my issue. Perhaps I need to keep looking.

There are a few fuses I didn't check (because I didn't know how to). They are the square looking ones that are in my engine compartment that have a clear plastic cap (pink & green in below photo). I don't know how to access the contacts to do a voltage drop test.

https://photos.app.goo.gl/9gnnLJvxRfTB33sX6

EDIT: I now know those square fuses are called J-Case fuses and the proper way to test them in situ is to pop off the clear plastic lid. I will try to do that in a few days.