I left my A3 for an hour after driving it normally, and when I returned I found the battery was almost completely dead. The car wouldn't start, and even the hazard lights were having trouble staying on.
I used jump leads from a friends car to get it started, and drove for about 30 minutes. The dashboard lights and dials would occasionally cut out while I was driving! Fortunately the headlights stayed on the whole time.
As soon as I turned the engine off the battery was dead again and the car wouldn't come close to starting.
Clearly an electrical problem, but where so I begin? Is the battery at fault, or the alternator which is meant to charge it? Some people have suggested a faulty starter motor might be the issue. I'd like to know the best way to diagnose the problem. It will be hard to get the car to a garage from its current resting place in the countryside! Thanks.
I did some simple tests to narrow down the fault, between the alternator and battery. Perhaps someone could help me draw a conclusion from the results:
The battery was taken out and charged. The car started (somewhat reluctantly) and ran for 30 minutes until parked, but after leaving the car for 2 hours after that short journey, the battery was dead.
With the charged battery connected, revving the engine did not affect the headlight brightness.
Disconnecting the battery while the engine was running did not stall the engine or effect the electrics.
The starter motor makes a short, loud whirring noise just after the engine starts. This has happened before though, with no noticeable effect on performance.
So... it needs a new battery, right? Unfortunately I do not have a voltmeter, and I'm stuck in the countryside!