David Sechy

Please bear with me. I’m 75 years old and bought my first Porsche in March 2019. It’s a 1999 Carrera. Great fun to drive. Problem is that the battery runs down and car won’t always start. I carry a charger with me so I can essentially jump start it. I have been embarrassed when I parked the car in a parking lot while shopping only to find that when I return the car won’t start. The battery was new when I bought the car. The guy I bought the car from says that the car has various computers that run down the battery when car isn’t driven. My son put a diagnosis on the car and it shows no codes. I’m wondering if I should go get the battery fully charged and then have a shut off switch installed?? Does that make sense? Any suggestions are welcome. Frustrating to have a nice toy that I’m afraid to take anywhere. Thank you.

NuttyProfessor

Hi Davey. Parasitic battery drain is not totally uncommon with Porsche cars of this age. First bridge to cross is to have the battery tested. Even though it is new, it still could be bad. Then, if the battery is tested fine, you'll need to locate the source of the parasitic battery drain. This is no easy task and so be patient. First, look at the obvious. When you pull the car in the garage, turn it off and shut the doors, wait around to make sure all lights turn off after a couple of minutes. If not, then you have a faulty microswitch in the door lock mechanism for example. Next, if the interior lights turn off normally, then the parasitic loss is coming from another source. Using a multimeter, you'll need to pin point the unwanted current draw by examining each fuse. Are you good with multimeters? If not, a simple DC battery checker from Harbor Freight will work too. Good luck!

Flat6 Innovations

@David Sechy
How long does it take the battery to die?

Do you know the procedure to "put the car to sleep"?

808Bill

Is your alternator charging?

wildbilly32

Welcome David and good on you for your first Porsche. You have come to the right place. As above start with the battery check. Flat6 Innovations above is super knowledgeable on these cars as are many others here.

Woodman71

Mine had similar symptoms and it was the wiring harness. Seems to be a pretty common issue.

pdxmotorhead

Make sure the trunk light is turning off.. For whatever weird karma reason, every
german car I've owned has had a flaky trunk light.

Use an AGM battery, they wont leak, don't give off gasses and they have about 30% more
reserve capacity, and weirdly enough ,, farm supply stores are the place to get them.

I used the Exide AGM's in my BMW's they are horrible for draining batteries when they age.. Always good luck.

phease

Davey. Congrats on the new to you Porsche. There might be a short inside the battery. I had a similar problem years ago. Car would start, I would drive a few miles and then when I tried to restart, not even a click. One more thing to check. Cheers! Pat

DBJoe996

There is nothing unique as far as a battery to a Porsche than any other car on the planet. At 75 years old, you must have owned several previous cars. None of them ever needed a new battery? Don't waste your time getting it "charged." If the alternator is working correctly it will provide all the charge you need. Have someone check the charging system for proper voltage output and get yourself a new AGM battery. Locked or unlocked, the car should be able to sit for more than 2 weeks and not drain the battery to the point where it will not start.

Most auto parts stores will check your charging system and install a new battery for you for free.

garrett376

I've had 3 996s, and I still have two of them. Outside of alternators dying, or batteries getting tired over the years, all three had parasitic drains that would kill the battery in time. 2 of them had glove box light switches that kept the light on at all times, and 1 had a shorted lumbar position motor in the driver's seat that would drain the battery pretty quickly, but not blow a fuse. A little time spent doing current drain testing while pulling fuses and unplugging things in the circuit solved all the issues.

Flyfishnick

I also had a parasitic drain from the stereo's amplifier (stock amp) that was wired wrong and it never turned off. If you have an aftermarket stereo deck, maybe feel the amp in the frunk in the morning (after sitting all night) and see if it feels warm. Obviously there can be lots of little gremlins, but this one was eating away at me for weeks until I (really, my neighbor) figured it out.
Just an idea...…...
Good luck and enjoy your ride

fpb111

Horsepwr

Take it to the local shop and have the battery load tested. If it passes that then test the alternator, if that passes then you need to start to find the drain. I leave my car parked from October to April and the car fires right up, not jump needed so something is definitely off.

docmirror

Couple of comments. First, yes - these cars can be hard on batteries. They have continuous parasitic draw, even when they are in top condition. The chart above is nice to know, if one has the tools and knowledge how to measure current draw. If not, see a electrical specialist.

The voltmeters are notoriously inaccurate, but can be useful for a trend, even though the absolute numbers are not exact. Here's a simple test you can run to do a basic check of the charging system:

Unlock the cold car, sit inside, put the key in, and watch the voltmeter. Do not press the brake pedal or clutch. Turn the key to the 'on' position but NOT 'start'. Make a note of the reading. Ideally(but no guarantee) it will be just over 12V. This is your reference, 'no charge' state. Crank the engine, and start the car. Let the car run for a few minutes, there will be a motor running during warm up, wait for that motor hum to go off. Turn off ALL accessories, no radio, no heater, AC, lights, wipers, brake lights, just let it sit there for about 5 minutes. Record that voltage. Ideally it will be just under 14V(but again, for the pedantic out there, this is NOT a guarantee). What we are looking for is that the charge voltage is about 1.5 volts over the resting 'no charge' voltage from before. The only load at this time, is the engine load for the fuel injection, fuel pump, and ignition, just the basics to run the car. If this is ok, proceed below. If it is not ok, then you have a charge issue that needs to be sorted out. Could be many things, but at this point, we will assume you have a good charge voltage.

Next, we are going to test the battery ampacity. Go for a drive, and do not shut the engine off during the drive. We want to fully charge the battery so that there is no question your battery is fully charged. You could do this with an external charger, but going for a moderately long drive will get everything warm, and allow the alternator to get its workout charging the battery fully. You may note as the battery gets charged that there will be small changes in the voltmeter. It will become more 'sensitive' to engine speed as the battery reaches it's topped up state. When it is charging hard, the load on the alternator and wiring will damp out that sensitivity, but when fully charge you are at 'float' voltage, and small changes in engine speed near idle will be reflected in the meter movement. Hopefully you will drive enough to note this sensitivity in the meter needle. Do not turn the engine off during drive, or when you get back home!

It's time to load the battery. The alternator in all modern cars will struggle to put out enough current at idle to support all the accessories. So, we are going to load it hard. Turn on the lights, wipers, AC to full blast, radio, open a door, and step on the brake. Watch the meter as you do these steps, and you will see the meter needle go down toward 12V(or lower if that was your reference). If the alternator light comes on at any time, you have exceeded the amp delivery of the alternator, and are pulling from the battery. It may be hard to see, but the alt light may barely flicker with everything turned on. The voltage should be very close to the 'no charge' voltage from your first test. You may also note the idle will sound a bit different as the idle air control circuit opens to maintain RPM with a higher load on the alternator. This is good.

Now keep watching the voltmeter, and slowly raise the RPM with throttle(no need to drive, just rev it carefully) to about 2500. The voltmeter should recover slowly and stay steady at about 14V again. It will be a bit lower than the float voltage, but it should be close. If the voltage stays down near the 'no charge' voltage of 12V(or whatever your reference was), then you still have a charging problem, but it is related to current draw, and not regulation. More likely a bad alt, or even a slipping belt could do this. (belt slip is pretty rare)

If this in-car test works out pretty well, have the battery load tested at O'reillys or another car place. Not just the voltage, but they have a load tester. I also like to check the Specific Gravity with a hydrometer, and they are very cheap way to test the chemistry of a battery.

https://www.oreillyauto.com/detail/b.../4742207?pos=0

If all this checks out you may simply be not driving long enough. Try some distance drives, and don't let the car sit more than 3-4 days. If it works out, then that means drive more.

Horsepwr

[QUOTE=docmirror;15958093 Try some distance drives, and don't let the car sit more than 3-4 days. If it works out, then that means drive more.[/QUOTE]

You should absolutely be able to let these cars sit longer than 3-4 days....