Flat battery - cause?

[hsyben]

I usually drive my 2003 Z4 2.5i at least once every week without any problems - just a lot of fun
However, I have left it twice for two weeks without firing it up and found the battery drains flat - the electric locks won't even work. The battery is only a year old and I haven't left any lights on.

Any ideas of what could be draining it please?

 

[Special Kay]

My guess would be that "I presume" you don't leave your car on a trickle charger in between drives. It's usually bad for any battery to be run flat, it kills the battery inners, it affects the charging/recharging abilities of the battery too. You say the battery is only a year old so should still be under warranty. I would try charging the battery, if it doesn't fully charge, take it back for an exchange battery. Sorry I can't be more technical or helpful, I'm sure someone more knowledgeable will come along soon and help you further.

 

[enuff_zed]

Check the light in the centre storage cubby between the seats.
Make sure it switches off when nearly closed.
If not, then check the bottom of the opening door. There is a small plastic lug on the bottom that activates the micro-switch for the light. This is easily snapped off, so the light stays on.
If broken then obviously start by disconnecting the light until you can fix/replace it.
If you cannot find a good condition lid then it is possible to remove the lid, drill a very small pilot hole to prevent cracking, then fit a small self-tapping screw and adjust it's length to activate the micro-switch.

Of course, this may not be your problem at all.................

 

[colb]

Could well be something draining the battery like enuff_zed describes however with the engine running put a volt meter on the battery terminals and see what voltage is being put out by the alternator, you should see around 14volts if its charging ok. If its charging ok then next move would be to check for a battery drain, take a look on Youtube for info on how to do this, if it is a battery drain it will involve taking fuses out to see which circuit is responsible and then checking the wiring and connections to the offending item.
https://www.youtube.com/watch?v=HqxB4Ete17I

 

[hsyben]

Thanks for all of the advice. I didn't even know that there is a light in the center console, but it seems to switch off ok. It has an aftermarket dashcam and it occurs to me that this is worth checking. I'll go down the battery drain route.

 

[Special Kay]

I reckon you've found your culprit. That happened to me earlier this year. Resulted in a new battery in my case :headbang:

 

[Jamezee]

Check the light in the centre storage cubby between the seats.
Make sure it switches off when nearly closed.
If not, then check the bottom of the opening door. There is a small plastic lug on the bottom that activates the micro-switch for the light. This is easily snapped off, so the light stays on.
If broken then obviously start by disconnecting the light until you can fix/replace it.
If you cannot find a good condition lid then it is possible to remove the lid, drill a very small pilot hole to prevent cracking, then fit a small self-tapping screw and adjust it's length to activate the micro-switch.

Of course, this may not be your problem at all.................

Just found this exact same problem on my coupe today jammed the swith off until i can get new or replacement parts

 

[enuff_zed]

It's actually quite a simple fix. Sounds a bit cowboy, but honestly you can'tt see it!
Remove the door. There are various instructional links on how to do this. If you can't work it out, PM me.
Once the door is off, use a file to smooth down the snapped of lug remains. Then use a small drill bit to make a pilot hole through the lug base. If you don't then you run the risk of splitting the plastic. Get a small self-tapping screw, about an inch long and gently screw it in to the bottom of the door until it projects the same amount as the old plastic lug did.
Refit the door.
The screw operates the microswitch the same as the old plastic lug. And unless you know it's there you'd never know.