Porsche Boxster - battery keeps going flat

[alih44]

Hi everyone,
hoping you can help as just about had enough of my car - if i don't drive the car for 3 days the battery goes as dead as a dodo!
it had a bew battery about 6 months ago as it went flat.

then a few months ago it started playing up and went flat again - it went into a garage where they ran a load of diagnostic tests and could find no battery drain, so they said it could be the battery so i replaced the battery.

couple of weeks ago i didn't drive the car for about 2 days ( after a long run of over 45 miles), it just about started but the alarm started going off and took a while to switch off.

can since then has had quite a few long runs and its been ok. left it for 3 days and now totally dead!

so so fed up - anyone got any advice please/thoughts? and yes everything was switched off lights etc and the car waslocked.

[jamesogt]

When I park mine for any period of time I remove Row B and C Fuse 3.(It is also garaged and trackered)

Seems to help.

Cheers

[alih44]

thanks but i really shouldn't have to do that after 3 days
-i use to leave it for 2 weeks on holiday and it was fine - i had to use the key to open it because of the power save

[clockworks]

If the battery isn't faulty, there must be an excessive drain somewhere.

It's a case of pulling fuses to find which circuit is causing the drain. Either pull fuses and leave for a few days, or put a meter in series with the battery.

[Axel987]

porsche batteries are st, swap to a Sønnak battery - I did.

[alih44]

hi clockworks as i mentioned there has been diagnostic tests run overnight by a garage previously and no drain was found - this would have included checking all the fuses

[swimd]

I'd swap the battery for something decent... Bosch, Varta or Banner.

Avoid Moll at all costs (= old OEM for the 997/987 batteries and what you get when you buy a battery from the OPC. Porsche switched to Banner for the 991 onwards).

[Henry Fiddleton]

Wait, you got a new battery and it was ok for bit?

My MX5 had a similar issue - turns out at high revs the alternator was dropping charging voltage.

Are you sure your alternator is charging your battery completely?

[alih44]

i assume the garage would have checked for that - i know they ran the diagnostics overnight.
i don't believe the issue is the battery there is something else going on that is causing this issue

[Henry Fiddleton]

alih44 said:

i assume the garage would have checked for that - i know they ran the diagnostics overnight.
i don't believe the issue is the battery there is something else going on that is causing this issue

Assumptions are the mother of all..

Also don't rely on that over night check - sounds dubious. What exactly did they do?

My alternator also passed the voltage test at idle. Its only when I told them to check it over 4000 rpm it showed a drop.

[clockworks]

Have you tried using a decent battery charger/conditioner? Get the battery fully-charged, then see if it still drains down in a couple of days.

I've never had a faulty alternator, but it certainly fits the symptoms. Using a battery charger would rule out the alternator if it still went flat within a few days just sitting there.

[alih44]

the battery was fully charged as i had done a long run in it on the lastday i used it.

the garage did full diagnostic tests on it - i've booked it into another garage to see if they can find the fault.

thansk everyone for your input its much appreciated

[thegoose]

alih44 said:

the battery was fully charged as i had done a long run in it on the lastday i used it.

the garage did full diagnostic tests on it - i've booked it into another garage to see if they can find the fault.

thansk everyone for your input its much appreciated

Just reconsider what you're saying here - sure, IF the alternator's working correctly then the battery will have been fully charged after a run. However, if it's not working at higher revs (which is not a common test to perform) then after your long run the battery charge will have been significantly diminished as the car will have been using electricity from the battery not the alternator.

Ask for a test on the alternator throughout the rev range.

[clockworks]

I agree with the above post. Get the alternator fully tested, or charge the battery with a charger.

It's got to be the battery (either not holding a charge, or not getting properly charged because of an alternator fault or a bad connection), or a high drain.

Finding the cause of this kind of problem isn't that difficult, but it can be very time consuming, hence expensive if you are paying someone to do it. Takes a methodical approach, and a lot of patience.

If it was me, I'd charge the battery, then test it under load.
Next, I'd check for good continuity between the battery and the bodyshell, and the engine and bodyshell (earth staps).
Check the battery voltage with the engine off, at idle, and at high revs.
If all the above are good, start pulling fuses, preferably with an ammeter in series with the battery.

[AndrewsCayman]

Have a look at the where the positive lead connects to the distributor box behind the glove box. It can get corroded there and make it seem like you,have a flat battery.

I just did a more detailed post on the same subject because I have the same problem and found a potential solution on Planet-9. I hope to get it sorted next week at the OP.

[cost-down]

i had a 2000 996 and a 2001 boxster 986 both lost battery charge after a few days unused .... what i have done is fit a 12V 95AH S4013 Car Battery BMW, JAGUAR & MERCEDES Bosch S4 013 019 bosch battery (fits the tray but you will need to alter the bolt down retaining clamp) i also disconnected the alarm back up battery (just four small screws on the alarm which allows access to the inside of alarm the backup battery is just plugged into the circuit board this is on the right of your battery as viewed from the front of the car ) as this battery is over fifteen years old and is kept charged from the main battery after 15 years this must be in a poor state (the alarm still works fine but does not work with the main battery disconnected ) now all is well ...... this is only a suggestion but it worked for me.....

[Porsche911R]

A good battery and working system will last 4 weeks no issue untouched.

[cd1957]

Hi Alih,by reading everything you have gone through,there has to a drain on the car.I have just had Boxster in workshop for 6 weeks and it never went flat.
The car needs to be fully warmed up and then meter connected,without braking circuit,drivers door lock needs to be latched and car locked with remote.The amp draw will be around 1amp initially and over approx 1 hour should drop to 300ma if all ok.
Chris

[DJMC]

I'm guessing he's sorted it by now... hopefully!!

[mikefocke]

A guide to the drain on a battery is within this web page. Credit to several contributors. https://sites.google.com/site/mikefocke2/batteries

A common battery drain cause is some aftermarket car-location tracker or improper aftermarket accessory installation.

Another is the ignition switch not truly shutting things off.

But the first thing to do is to verify the alternator's output. Measure the battery voltage at 3000RPM (13.4 range?), the voltage after shutoff (12.8 range?). Compare with the tables provided.