ARGH! Why does my ****ing battery keep going flat?

[dillenger1]

Try isolating the starter.Mine is behaving the same,It turned to be the starter.I even took it apart ,cleaned and degunked everything,no change.Check for post insulation or lack there of.

[Vincent Waldon]

my golf had a bad diode for as long as i have owned it .....about 2 years. and i never had the battery drain on me. i dont think its the diodes

Diodes can fail open... in which case they generally cause no symptoms other than a decrease in the available output power of the alternator.

They can also fail closed... in which case they will usually drain the battery by causing a direct path for current thru a field winding.

[molgrips]

Every couple of hours of driving, roughly, the tach goes a bit crazy for 5 minutes and then returns to normal. It's the alternator, cos if it comes back in when I'm idling and the fan/lights are on I can hear the engine note dip.

Stereo is a basic small one, nothing fancy.

Something else I noticed today - the central locking keeps making that noise it makes for a few minutes after I lock the car, but I heard it again today a good three hours after driving it last.  This could be the problem.

[the caveman]

Something else I noticed today - the central locking keeps making that noise it makes for a few minutes after I lock the car, but I heard it again today a good three hours after driving it last. This could be the problem.
___________
Very possible. I had a golf that, because the central locking had a leak, and didn't lock the trunk, the customer didn't know the truck wasn't locked, and lo- dead battery. The vacuum/pressure pump for the central lock has a function that shuts it after a 30 secs. if it's still running. however it sounds like yours isn't working as it should.

[handedyourhat]

I had a problem with my trunk light staying on it took about 1 day of charging the battery back up to full charge and the battery would die again, I removed the altanator from the system and I still had quite a large arc at the batt terminal  :shock:  so I got a thinkin, I replaced my trunk lid a week before and had no idea how the inside trunk light turns on and off , I still dont !!!, so I removed the light bulb from its holder and I haven't had a problem since :lol:  :lol:  :lol:

[Smokey Eddy]

Wow. I'm happy for you but what a head ache! You won't forget to check that ever again next time you're having batt troubles. Takes two seconds to check but, obviously, easily overlooked.

[rubadubdub]

Given the fact your tach goes mad the following is unlikely but just something else to consider if all else fails...

My dad had a problem with his mondeo battery occasionally discharging.  I traced it to a leaking rear light which would fill the boot up with water only when the car was parked bonnet downhill whilst it was raining, which created the short which drained the battery.

My reason for mentioning it was you said you've tested and couldn't find a constant drain on the battery.  However if you have electrical circuits which are getting wet occasionally the drain may not always be there.

[Smokey Eddy]

My dad had a problem with his mondeo battery occasionally discharging.  I traced it to a leaking rear light which would fill the boot up with water only when the car was parked bonnet downhill whilst it was raining, which created the short which drained the battery.

That doesn't sound very unlikely to me! that's good advice. These lights do leak frequently when they age a little.

[molgrips]

Hmm.. interesting.. it does seem intermittent. I will keep an eye on when it happens next.