I have a 2000 Audi 2.5 TDI which suffers an electric drain somewhere in the system, if I don't start the car for 3 days the battery will be too low to start the car. I now carry a spare battery in the boot. I thought a batterybrain was the answer to my problems but what happened was that because the battery ended up being disconnected overnight when I then started the car it set off the car alarm, which could not be muted. I contacted my local Audi garage that said that because the battery had been disconnected when I came to restart the car it thought it was being broken into. There was no way I could isolate the alarm and it would be an expensive job to access the alarm. They suggested I charge the battery overnight and try again the next day. Fortunately, this worked. Batterybrain were very good and refunded the cost of their product. However, I consider myself lucky that I did not end up with a big bill at Audis. My concern is that with modern electrics on cars could fitting a batterybrain cause other electrical problems like with ECUs etc that would need garage to reset.