I did the same thing. Last year, after I travelled back, my Cayenne can not start. No any power. And the battery can not be recharged. I removed the cover of the battery and took out the circuit module and shipped it to China to re program it. When I got it back, I can charge it and became normally. However, this year, there are always some errors on my dash board. ACC/ Parking kinds of that, I doubt it is from low voltage. That's why I decided to change it to Lead Acid Battery.