Battery keeps dieing?

[Junglistjed]

Its a 1986 316 and the battery keeps dieing, the car isn't currently being driving but i will start it up and give it a run around now and then, something is draining the battery and im not sure what? no lights or anything are on so really not sure :/

Any ideas?

[Speedtouch]

Have you checked the boot and glovebox lights actually go out? These are a common cause of mysterious battery drain.

Disconnect one terminal of the battery and use a multimeter to measure the drain current with everything switched off - it should only be in the order of a few mA.

[Junglistjed]

I haven't checked the boot light actually! what would cause them to stay on after the car is off and locked though?

cheers for the reply mate

[Speedtouch]

Duff plunger switch - sometimes they jam in the on position.

[jmc330i]

Could also be the boot latch wrongly adjusted - mine was actually broken so the boot lid didn't shut properly even though it looked fine and locked as it should.
My alarm kept going off as it detected the battery drain from the boot light staying on.

[jonny323i]

This brings in the topless method to check the boot light "lock the mrs in the boot and see if it goes off"

[pud1]

How quick is it draining it and what do you mean by a run. Are you putting enough back in it. How old is the battery, what type is it-wet, gel. Borrow a current clamp and check the output of the alternator for starters- current and then voltage with a meter, give it a good run -say 20 mile round trip with all the loads off ie lights, fan etc. Get it back in the drive and put a meter in the battery line on low amps(milliamps) and see if there is a parasitic drain. If there isnt it is more likely to be a sulphated cell. It wont be enough to stop the battery accepting enough charge to be useable but it wont accept enough charge to hold up during lay-ups. Batteries are fickle things. Been working with them from design to maintenance and I still learn something new every day.
Ps. It is a cranking battery and not a deep-cycle(leisure battery) isnt it. What does the label say. Is the number a recognised fitment option for the car.

[pac1982]

This brings in the topless method to check the boot light "lock the mrs in the boot and see if it goes off"

although the above method is the best, an easy way is to remove a rear light cluster and you can see in to the boot with the lid closed

or what I have done before is set my mobile phone to record video and leave it in the boot while you open and close it, play back the footage and you will see what's going on in there while the boot is closed