Had the same problem for about three weeks now and really don't know what to do. My car seems to be losing the charge in the battery overnight and when i try to start it in the morning, the car won't start. No lights come on, and there's no sound from the starter motor. If i jump start the car, then everything works fine. I've had a new battery and new alternator put in recently (2 weeks ago), so i don't know what it could be. I called out an auto-electrician to look at the car and he checked for every conceivable battery drain he could think of. It didn't appear to be the sound system, the alarm, the clocks, or the back boot light being on or anything like that.

He seems to think that it may be something that is coming into play when the car is moving and asked me if the car ever went dead as i was driving it down the road, but this has not happened to me. Does anyone have any idea what the problem could be?

 

Diode in the alternator mate.

Had this a couple of times on mine. Find out which one you have and replace it. The Hitachi one is the big 70amp job and is quite expensive the other 2 types aren't so bad though. Halfords carried all of them in stock when I last had to change mine

 

Like i said it's got a new alternator and it's definitley charging up as the electrician measured it to see if it was charging. Any other ideas?