After you resolve your current situation, install a 12volt battery lead.

Installing 12v battery cable

Documenting the install of a cable to access the 12 volt battery from outside the vehicle. There have been many posts about this project scattered around the forum. This will allow you to maintain the 12 volt battery and also give you an access point outside the frunk which WILL NOT OPEN if you...

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Posting back in case this helps anyone else, definitely learned about another option for accessing the frunk when 12v battery is dead...

Audi sent a tech to my home and he first tried the jumper in the fuse panel. As everyone has mentioned here, it didn't work to get power to the frunk to open it (I have a 2023). However, he got it open another way - I believe he removed one of the other fuses and inserted a bare wire and hooked his booster to it to back-feed the power (my words, not his). It worked!!! He was able to open the frunk so we could put a booster on the battery and power up the car.

The car had sat for a whopping 9-10 days without driving. It was unlocked and unplugged (80% charge on main battery). He said the 12v battery was only registering 0.7v and likely has failed.

Waiting for a tow but we can at least drive the vehicle onto the truck by using a 12v booster temporarily.

 

I believe he removed one of the other fuses and inserted a bare wire and hooked his booster to it to back-feed the power

When you head back there, please ask them! This would be extremely useful and I can stop carrying air shims and a 10mm wrench in the back of my car.

 

This question may be answered on this forum, but please remind me when the 12 volt battery is recharged…from the main battery when the car is turned on or being driven, or when the main battery is plugged in being charged?

 

Checking the voltage with my OBD11, the 12v seemed to charge consistently when the car was 'on' but parked up.
I didn't get time to do a before/after driving test, unfortunately.

 

Picked up my car from the dealer today and was able to get some additional information from the tech on two topics:

1 - How he opened the front trunk via the fuse panel (my car is a 2023 and the 12v battery was completely dead)
He was able to use an empty spot in the fuse panel (left/driver side foot-well - see pic of exact location). This was his positive connection point and he grounded to the large metal door latch inside the door frame itself. You can see that his reader is picking up the battery voltage from this location. He attached jumper wire to this location and that's where he hooked up his booster to get the front trunk open. He even gave me the jumper wire in case I run into this fiasco again!

2 - How to possibly prevent the issue in the future
Audi corporate recommended a maintainer, even though my car was sitting for a whopping 8-9 days. The tech indicated that turning on the car (on/off switch) would charge the 12v battery - and could be used if it's going to sit for long periods of time (obviously you'd have to be at the vehicle in person). See the final page of the attached technical info they gave me that I believe explains how this works.

There was another thread about how activating climate control might have the same effect - I think it could if the "HV network" is activated by doing so.

Hopefully this info is helpful to someone - at least there's an option to get into the front trunk of a pre-2024 that doesn't require air shims and a wrench!