Hi I'm fairly new to the site and if possible would like a little help to rectify an annoying issue on my 2005 2.5Tdi auto.

A few weeks ago the battery went flat for no apparent reason, I hadn't left the lights on, I'd checked the interior lights, glovebox & boot light - all appeared in order and weren't left on for any reason. Anyway I jump-started it and it started fine, took it for a brisk drive came home, left it over night and everything was fine. I've been to Oxford and return to Manchester since and then Manchester to Newcastle no problems. Then last night, I finished work at midnight peeing down with rain and...........yup! Flat battery!!!! Jump started it again and it was fine all the way home, the headlights were bright, all the electrics work.

First thing I thought was ok 8yrs old perhaps time for a new battery??? But I can't get my head around the randomness of when it happens. I thought if the battery was dying it wouldn't start period?

Second thing - I've heard that the radio hard-drive can flatten the battery randomly? is this the case? If so how would I stop it? Sometimes when I switch off the ignition I can hear the faint whirring coming from the radio??

I'm gonna test the battery with the meter, do any of you know what the readings should be for it at rest (i.e. what drian the electrics have when keys out & locked)

I may just be over complicating thinks and just need a new battery at the end of the day but would like a little advise

Thanking you in advance

Jason

Some things to look for first.

1. Can you hear the starter motor trying or is it simply nothing?

2. When it won't start are the main lights bright?

3. Are the connections on the battery very tight?

4. Again when it won't start is there any electrical parts that work (radio etc)?

5. Immobilizer?

6. Check boot light switch (this can be intermitant).

I am not saying that I can find an answer and sorry if you have already tried the above but I was looking for a potential bad earth connection and hopefullyit is not item 5.

Good luck.

Hi Danny,

1. It does try to start, but very very sloppy/slow turnover, then it dies. Can go days / weeks without having an episode.

2. Yes the headlights are very bright.

3. Battery connections have been checked and aren't corroded & are tight

4. Yep, radio will work, dash lights up, interior lights.

5 . Doubt it could be immobilizer otherwise it wouldn't try to turn over.

6. Boot light switch checked (by puttin the rear seats down & looking through) light off switch appears to be working fine.

Just done some tests with my electrical tester -

Engine off all electrical gizmos off = 12.46V

Engine running no gizmos on = 14.39 - 14.44 when applying revs

I've left it locked now for an hour, with the bonnet on the latch. Will check to see if there's any drian once all systems go to sleep.

Oh & by the way bloody thing started 1st time of asking GRRRRRR!!!!!!

Edited 16 May, 201313 yr by Royrover

Battery off load at 13.46v is a tiny bit low (12.75v for optinmum and charging at 14.39v is good) so that should not be a problem because if it was turning over slowly it would be lower. This points to a bad connection. Please check the battery to earth (body work) connection. Is there any corrosion on the body work?

As a second check on the battery if (when) it happens again reheck the battery voltage. If it is as above then again I would think it is a bad connection to earth or on the starter motor, it will not be the coil to the starter motor but he main cable on the starter motor.

The other possibles are but unlikely are a loose cable/connection/control on the alternater.

Others on here will most probably have better knowledge and hopefuly point you in a more accurate direction if the above does not get you anywhere.

Again, good luck.

VAG batteries i.e Varta are only good for around 5 years, the handbook advises you change them every 4 years.

Your alternator pulley clutch could be on it's way and this will stop the battery getting enough juice to re-charge itself.

Jason, I had the same problem.

Here is what I did,,,

Where the battery sits, it was 2 inch deep with water.

I took the battery out and removed the rubber bungs in the chamber.

I replaced the old battery with a new one and everything has worked fine since.

I hope this helps.

Thanks for all the replies guys, had the battery tested & it was goosed & not holding charge properly. £££ later and new battery later all is well.......for now! Incidently I looked under the battery tray & it was bone dry, gave the rubber bungs a clean while I was there.

Don't just clean them, rip them out completely.

Have a look at the following sticky thread.

http://www.briskoda.net/forums/topic/152490-water-ingress-problemsolved/