I've a 2002 E39 with a battery problem. It started a while back during the cold weather. I wasn't using the car much, and the battery ran flat a couple of times. I figured that was to be expected, and following a re-charge everything seemed fine. I checked the voltage when the car was at idle, adn it was about 13 volts or so, so I figured the alternator was working. However, more recently the battery has run flat more often. I don't use the car much, and the battery was over 9 years old, so I figured the cold weather had finally killed it off. I went a bought a replacement.
I still having problems. I ran flat again today - last used the car on Saturday. I had to unlock the boot with the key, adn the voltage was about 2.8 volts! I recharged it for about an hour, and then it read 11.6 volts. I tried to start the car and it didn't have enough juice - just got a ticking sound. Read the voltage again and it was down to 10.2 volts. A couple of minutes later and it was 8.6, and dropping!
Have I been sold a dud battery? It seems like something is draining the power. Are there any likely suspects? Or an easy way to work out the culprit?
Cheers