Hi there I have a 2009 Octavia 1.9tdi and I am having a problem with the battery goes flat over night the battery and alternator are fine so I am stumped as to what it is if any one could help

Some serious battery drain for it to go completely flat over(one)night.

 

How do you know battery and alternator are fine? and have you tried fully charging the battery using an external charger?

 

How old is the battery?

 

Do you have any audible alarms sounding? (not the main alarm).

 

Any dashboard lights remaining lit? (check after dark).

Go out in the middle of the night, several hours after the motor's been switched off and parked up.  Is a fan running?  Are the lights on?

 

The usual voltmeter checks will show if the alternator is good.

 

Something must be drawing 3A or more continuous for the battery to go flat overnight.  An ammeter, a wiring diagram, and a careful sequence of fuse pulling could narrow the list of culprits down.

 

It could be a wiring fault in a circuit protected by a heavy fuse, and letting enough juice flow to earth to flatten the battery without blowing the fuse.  That could constitute a fire risk.

 

A car battery will not stand going flat lots of times before it goes into 'deep discharge' and refuses to hold a charge any more.  A automotive battery specialist can check this for you.

Firstly assuming you have checked that the alternator charges at 14.3 volts measured across the battery terminals.

Just because you get it started and it runs around all day, restarting without apparent problem does not mean the battery is not in a terminal state.

It may be a bad cell, with just a small capacity, enough to restart after one hour, but internally damaged and self discharging such that after 12 hours its dead.

To check, disconnect one battery lead when you come home, reconnect next day when it would normally be flat. If it is flat, then its the battery thats u/s.

Otherwise then look at the current being drawn when stood, engine off and all things electrical turned off and trace the culprit electrical drain.

Retract the boot cover and check the luggage lights go out.

May be a faulty switch which could manifest itself as the rear wash/wipe not working and/or boot locking issues.

Even if the battery was OK, having it flat every morning will have seriously compromised it so even if there is another fault you will still probably end up buying a new battery