1986 928S2 (Euro)

Symptoms - the battery drains completely overnight. Fully charged to 11 point something volts.

The problem is that I can't detect any significant drain. I have checked between the battery ground connection and the ground post with 3 different multimeters now. All show the same. A few 10s of mA draw. Switching stuff on makes the draw increase as would be expected. That's not going to cause an overnight drain from full.

I've also replaced the battery with a new Bosch S5 - no difference whatever.

It's like something is intermittently switching in and causing a huge drain. Never when I'm there, of course.

Has anybody got any thoughts at all where to look or if I might have done or missed something stupid?

 

Have you watched the draw after locking the car, might be an alarm related issue?

 

If you check the voltage in the morning before doing anything else (like trying to start it) what is the voltage? Many, many years ago, a friend had a similar problem on a 914. Turned out when he closed the cover over the battery, the cover made slight contact with there battery terminals and drained it. Just a WAG.

 

A fully charged healthy battery should indicate 12.6 volts with a reliable voltmeter in the static condition. With the engine running and the alternator/voltage regulator in good condition it should indicate around 13.5 volts or so.

A static battery showing 11 point anything volts when "fully charged" could possibly be buggered.

 

did you shoot the CE panel with an IR gun?
drive the car ,
remove the parcel tray and the Ce panel covers ,
put the windows down close the doors let the car sit for 20 mins,
use the IR gun to see what relays are hot without opening the door.

as noted the battery may have gotten damaged.
So get a fresh battery first

 

Just to answer some of this

the battery is new, new. Changing the battery made no difference.

The car is in a garage and I’m not locking, unlocking it and I’m not using it because of the problem.

There’s no alarm fitted.

The battery drops from fully charged - 12.7 or so - to 11 point something overnight. Definitely drained.

Good idea checking for heat in the CE panel

 

if your new battery has gotten discharged then it could be damaged
NOTE charge the battery with a 6 amp charger for 4 hours , after standing for 24 hours,
your standing voltage SB 12.8V if its lower than 12.0 V,
then the chances are good your NEW battery has been damaged by a discharge event.
Make sure you have a good multi meter as well

 

Your battery may be OK but your syntax could do with a boost!

Suggest you check the diodes in your alternator.

 

Sorry - I was typing in a pub :-D

I'm sceptical that the battery is the problem. It's a good quality one, two days old and my fancy charger doesn't say it's faulty (it's always been quite good at that).

For full disclosure, I made a new engine loom because the old one was a mess. I do (normally) know what I'm doing. It's been fine for several months so I doubt it's that. But....

 

Does your car have the memory seats? I solved a drain on my car due to a faulty memory seat module in the driver's seat. Symptoms you may have an issue would be that the seat controls do not work in all directions prior to repair.

 

Nope. No memory seats. I think it's too old.

 

if none of the CE panel areas get warm . fuses or relays, after letting the car sit for 20 mins
then the alternator is the next thing to remove

 

This little sucker tells me about my battery condition..car and motorcycle.

Has no significant drain, and lets me eyeball charging conditions -at- the battery.



I can pull data from it from watching the tv in the house..easily 50' away plus walls

 

Just to eventually tie this up - it turned out to be a faulty Alpine amplifier that runs a sub in the boot.

The problem was intermittent. I used to be a repair agent for Alpine just to add to the irony. Something leaky in the switching circuit was powering it up - probably temperature dependent or similar. I've not fully diagnosed the fault but that seems to be the origin.