Having read about it happen to others it finally happened to me!
I experienced the amazing feature of Audi design, where if the car was locked with the key fob and the power supply is cut off, you cant unlock the boot physically with the key.
It was my fault really, I kept using the Webasto heater for 25 minutes before each day's driving, and I guess with the cold weather and everything the little lithium battery just was not getting charged enough after all that heater use.
So I finally pushed it over the edge and caused the low voltage cut off to kick in. Came back to the car and no power.
The battery low voltage cut off is an ingenious system with one flaw (due to being in the boot). The battery circuit switches itself off to keep enough capacity to start the car.
All you have to do is press the ‘on’ button
I could unlock the driver’s door manually and all the other doors. Luckily I have a ski-hatch with all the stuff removed. Using a wooden stick I managed to pry open the battery compartment door.
Still couldn’t see the button. So I taped a small mirror to the stick and moved it around until I could see the battery ‘on’ button. But how do I press the button? I decided I need a L-shaped stick long enough to reach the button. Luckily I had a cheapo metal broom stick with a plastic end and a hole to hang it up. Fishing around for something to jam into it to make a L-shaped stick I found an old plastic compass with a plastic screw-on cap to hold the pencil. So with a bit of fiddling this formed a ‘finger’ at the end of the broomstick to press the button.
After several tries (you have to hold down the button for a second or two to turn the battery back on) I managed to do it, pressed the key fob unlock and the boot opened.
Phewwwwww!
Now I know what a nightmare it must be to have the battery die and unable to open the boot. What a stupid design feature!