Seriously annoying battery problem!

[JPawson8]

I have a Passat 1.8 Sport Turbo on an S plate. Car ran fine for over a year with no problems at all then all of a sudden battery died on us for no apparent reason. Bought new battery from Halfords assuming it was a problem with the battery but now we have no end of problems with the battery draining.

If the car isn't driven for literally 24-36 hours, the battery dies and it won't start, although we still have lights, stereo etc. A few people have looked at it but can't seem to find the problem (have done tests on the battery and ampmeter on the battery etc). Ampmeter on the battery did show something draining the battery but no change when each & every fuse removed.

Anyone got any ideas?! Getting a bit annoying now, especially when I get the kids in the car & then have to get them back out again cos the darn thing won't start!!

[snapdragon]

After a run, check the main power cables to see if they are hot, if they are hot, they may be corroded and be resistive, this will stop full power coming from battery to start the car, and also reduce the charge going back in.

[JPawson8]

Thanks for that snapdragon! Will try that at the weekend once we have taken the battery out and charged it AGAIN!! Will let you know if this is the route of our problem!

Cheers

[Izalman]

I have some auto electrical experience, the problem sound like the diode pack/ rectifier (changes AC -DC) in the alternator may have failed. Classic symptom is progressive battery drain.
The rectifier in the alternator is permenantly connected to the battery live and if faulty allows voltage leakage when the engine is not running.
Not sure how accessible the alternator is, quick check - disconnect battery -ve check voltage between -ve cable and battery post ( make sure doors shut, radio off etc. Should have 0-1v max. If higher, leave -ve cable disconnect cables from alternator and recheck volts between battery post & cable. If volts reading drop to 0, sorry new alternator required.