Benzor

Hi RL -

Long time Porsche owner, first time 996. I've had a 944 Turbo for a while

I'm having electrical drain issues. It left me stranded the other night, and has been dead a couple time.

I took it to Autozone to test the battery, and they said it checks out ok. Battery is 3 years 3 months old, 790CCA unit from Walmart.

I was just in the garage. Battery was disconnected and reads 12.59V. I connected it, got in the car, and checked the voltage, was at 12V on the car's gauge. I started the car, let it run for 30s, then killed it. Battery gauge in car then reads 11.8V. I got out, walked around for 2 minutes, got back in, and car didn't have enough juice to crank.

Is it really possible I could have drained the battery in 1 start? That sounds like a massive electrical drain.

Similar story a couple nights ago - I had it on the trickle charger at home, drove it to dinner, parked it for 3 hours, and battery gauge in car read 10.2V when I got in - car wouldn't start.

The other test I had run was to charge battery up with trickle charger, then, disconnect it from car. Battery started at 13V, came down to 12.5V quickly, but then stayed there for 12hours.

Suggestions for how I diagnose this?


__________________
103k 996 C4S
Boston MA

Drisump

Sounds like it may be a dead alternator vs "a drain". If it's been like this a while, the battery is probably toast, despite what Autozone says. I don't know what kind of charger you have but if it's the maintenance type, you need an awful long time connected to top up a good, but almost dead battery (ie. Several days)When the alternator is dead, every minute the car runs is a drain on the almost dead battery. Alternator drive belt or bad grounds....could also be the culprit. Cheers BTW, this is an air cooled forum but your issue doesn't seem 996 specific.

theiceman

the only thing that makes this a 996 specific issue is the comparison data as what is expected.

if you put an ammeter in series with your battery ( ie disconnect one of the battery leads and hook your multimeter in between set to Amps ) . on ou cars the only draw we have is 4 or 5 millimaps that power the clock and radio memory in some cases.
The 966 probably has more draw with more gadgets like alarms, and other monitors.

I would start by doing this and reporting to the 996 community.

With the car running if you check you voltage at the battery and it is anything less that about 13.1 volts at idle I would say your alternator is toast.

Benzor

Will do ammeter test this weekend.

On Voltage at the battery, when running the in-car gauge shows 14V, but will test at battery.

theiceman

no that's fine its the same .. 14 v is perfectly fine ...

use this youtube vid to guide you , it is very good and quite funny.

blockhed

voltage regulator on the alternator seems to go and cause this, at least that was the issue in 996TT. It's a 40 dollar part, worth looking into.

blockhed

Benzor

Thanks Blockhed. Car is in garage and ready for diagnosis this weekend!

Benzor

Tried the parasitic draw test, but with battery at 12.07 volts (not enough to start the car) and couldn't find anything.

Now charging the car, will retry when charged.

Earlier, I had the battery down to 12.05V, but then over course of 4 hours came up to 12.37 volts (without charging) - now checking my voltmeters against a second one.

theiceman

can you explain what you mean by " couldn't find anything ?

Benzor

Sorry, what I meant by "couldn't find anything" is that there was a very small drain of 38mA, but there wasn't a large drain that would explain draining the battery. Am going to retest this evening starting with a full battery.

One thing I was puzzled by last night - the dash lights didn't come on when I had the multimeter in series with the negative battery cable. It was like the battery was disconnected.

PS - I have been to Cambridge / Gault ON!

theiceman

Be careful when having the multimeter in series. Too much current draw can blow the fuse in the meter or the meter itself.
38ma does not seem extreme. I wonder if something is turning on. Does the meter have the ability to record max current ?
You could also charge and leave disconnected. If it doesn't start the car the next day it's pooched. Can't hold a charge

Cool about Galt. I've lived here since 93. I hate TO and prefer it out here.

Benzor

OK, tried the parasitic drain test with a full battery (12.52V) and only came up with 40mA of draw.

That said, when the battery was reconnected, I could watch the voltage fall (with the car off) at 0.01V/s or so.

I will leave the battery disconnected for a couple hours, and suspect it won't fall off that much. My suspicion is that it can hold a charge, but not many amp-hours, pointing to battery replacement.

Benzor

Charge test at Advance Auto went fine, but they wouldn't do a load test unless battery is in the car. So will put it back in the car and then bring it over for a load test.

ADias

A 40mA draw with the car sitting (key off) is normal on 996/997. Actually, 45mA is currently more typical. The OP's battery is probably sulfated. It may be recoverable with a proper maintainer (CTek 4.3 or similar) or not. A new battery will be needed soon.

Air-cooled cars parasitic loads are usually very small (clock), but not the water-cooled. With their parasitic debit of 45mA they will use 1Ah/day of battery capacity, meaning that they will lose 15Ah sitting a couple of weeks.

Tip: lowest parasitic drain of water cooled cars is when they are locked with the cockpit alarm off. To do that lock them with the FOB, pressing the locking button twice - a long light flash is triggered when that happens instead of the usual double short flashes.