Any one know about cage electrics?

[Motu]

My daughter has a similar problem with her car - battery going flat for ''no reason at all''.She had the battery and alt output checked at my old shop,and was told they were both fine.I just check not 20 minutes ago - and the alt output is low.It is charging,but not quite enough.I have very seldom seen discharges draining batteries,it does happen,but not often - but altenators,startors and battries drag each other down...one is the culprit,putting load on another causing that one to crap out.

[Mully]

Thanks Motu. What should it be charging at? I would have thought 14-odd volts was more than enough?

Thanks,

[Motu]

Odd volts are not enough,more accuracy is required in electrical work.You need to check it under load,how quickly it cuts back,and what it cuts back to.Check starter draw as well - starting,charging and battery are all closely related,if one is below standard it will drag the other down....and out.

[Ixion]

..
Yesterday (when all my troubles seemed so far away), while the car was running, the battery was registering 14-odd volts. Once the car was off, it was registering 12-odd volts. I would have thought that was pretty much where it needed to be.

...

If the battery is only 12 volts with engine not running, it is defective or the charging circuit is defective. It should be at least 12.8V.

12V, it only needs to loose half a volt or so and starting may be problematic. My BMW will not start reliably if the battery is 11.5V.

One thought though. Do you have a boot light that turns on automatically when you open the boot? If so, check the switch is not stuck. I have known them to stick on, leaving the light on all the time (usually they are not wired through the ignition key). Of course, since no one can see in the boot with the lid shut, no one ever realises the light is on when it should be off.

[ynot slow]

Or the light in glovebox can stay on.

[Chooky]

Yea the boot light can stay on without no body knowing,that'll suck the battery down........Had a toymotor that did that once ...
Pull the bulb out and chuck it away...ya dont need a boot light anyway..

[Mully]

No Boot light.
No glovebox light.
Pulled the interior light (wasn't working anyway)
(it's a 1990 Mitsi Lancer).

[racerhead]

There is also a possibility that the alternator is faulty and dis-charging the battery when the engine is not running. The way to check this is with a current draw test which has already being described, using a multimeter set to dc amps.
When the meter is connected observe the reading-if its above .5amps theres a problem
To be sure its the alternator you will have to disconnect the main positive on the alternator and repeat the test, you should now have a reading below .5amps
If the reading is still above .5amps the next thing to check would be all internal electrics and the easiest way to do this is just pull fuses out one at a time checking the meter readings after every fuse. If you pull a fuse and get a reading under.5amps this is the item that is causing the current draw.

[BMWST?]

and you will need to charge the battery properly too now...1/2 hr running around aint enough....you may manage, but the battery wont like it and you will shorten its life...beg /borrow/buy a charger