"Normal" Battery Drain

[pabloification]

I've been struggling with rapid battery drain on my 981 and wondered if some gurus could help.

What I've tried:
1. Checking every fuses current in the footwell fuse boxes after the car has gone to sleep.
2. Bought a battery monitor (see attached for drain example).

1 highlighted to me that the only things draining current were the PCM and instrument cluster before the car went to sleep (0.75A total) but these went to 0A once the car went to sleep.

2 has shown the drain on the battery over 24hrs. The orange line is the voltage and we can see after a decent drive the voltage sits around 12.7V which would suggest the battery is fully charged. After only 24hrs this voltage has dropped to about 12V, which suggests the battery would go flat after only 3-4 days.

My main question is what else could be draining the battery? What can I check?


Thanks!
George

 

[Luddite]

I am NO expert sorry.... I guess the age of the battery may play a part and the life it has lived over time... i.e. used as a daily, or used very rarely, and whether kept on a float charger or not, thus quite a few variables to consider before thinking a possible electrical fault, other than drop in battery efficiency.

 

[pabloification]

Thanks for response - omitted a couple of facts...

New battery 6 months old, parked on street so not trickle charged, not daily driven (driven every three/four days but only to stop it going flat).

 

[911UK]

Thanks for response - omitted a couple of facts...

New battery 6 months old, parked on street so not trickle charged, not daily driven (driven every three/four days but only to stop it going flat).

shouldn't do that

i have some experience in this area !!

it could be a faulty battery ? it does happen
I would have said PCM drain but you've already eliminated this, but worth taking the pcm fuse out and then observing
- are you sure the bluetooth is off ? check by turning this off, it might still be on even with the pcm off !!!!
there is also https://www.pcmrepairs.co.uk

maybe it's the tracker, are you sure you don't have one ? i.e a former owner might have installed one and its disabled but still draining the battery?

otherwise check for any damp issues inside thar car that might be causing damp short circuit issues from a leak in the roof

then it's time for a look at the alternator and specifically it's diode

 

[pabloification]

shouldn't do that

i have some experience in this area !!

it could be a faulty battery ? it does happen
I would have said PCM drain but you've already eliminated this, but worth taking the pcm fuse out and then observing
- are you sure the bluetooth is off ? check by turning this off, it might still be on even with the pcm off !!!!
there is also https://www.pcmrepairs.co.uk

maybe it's the tracker, are you sure you don't have one ? i.e a former owner might have installed one and its disabled but still draining the battery?

otherwise check for any damp issues inside thar car that might be causing damp short circuit issues from a leak in the roof

then it's time for a look at the alternator and specifically it's diode

I thought as much...

After this caused a totally flat battery I spent a day going round the houses and the RAC had to use their jack to take off the wheel well liner and open the frunk (footwell fuse connection wouldn't open frunk with jump starter, car battery or RAC's jump starter or van), after which they used their kit to do battery and alternator health checks - both of which passed, so thinking I can rule out faulty battery and alternator for now (but correct me if I am wrong).

The screenshot of voltage data I uploaded is with both the PCM and cluster fuses removed from left footwell (B9 and B10 I believe). Tonight I've left them in to see if any difference.

Bluetooth is a good shout, how can I guarantee it is off without pulling the PCM power wire?

Previous owner reckoned no tracker but wouldn't know where to look. There isn't a fuse in the designated tracker slot so it has been incorrectly wired if that's the case.

Damp I haven't checked - I'll take a look given the volume of rain recently.

Thanks!

 

[911UK]

just turn off the bluetooth and see if it makes any difference

 

[TurboSandGT4]

Hi Pablo

Are there any aftermarket mods/features on your vehicles?

Based on my experience, 991/992/981/718 can be left for weeks on end without starting with no issues

 

[pabloification]

Thanks all - solved the issue.

Previous owner had an aftermarket exhaust controller wired into the permanent live circuit vs the ignition live so the controller was drawing 600mA-1000mA whilst the engine was off.

 

[Jay.]

Thanks all - solved the issue.

Previous owner had an aftermarket exhaust controller wired into the permanent live circuit vs the ignition live so the controller was drawing 600mA-1000mA whilst the engine was off.

Good job, mine had this too.

How did you trace it? I luckily saw mine despite it being cleverly wired and hidden amongst the normal wiring

 

[Alex]

If it were me I'd take the battery out and rerun the test you are doing without it connected to the car. That would eliminate if it were the car that's causing the problem. How much current does the battery monitor draw or is it self-powered? Make sure the battery is in the same condition (temp wise) if you test it off line, so in your shed or outdoor bog.

Edit: Just read the outcome but I'll leave my suggestion here for others to read.