Davey

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.

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!

@David Sechy How long does it take the battery to die? Do you know the procedure to "put the car to sleep"?

Is your alternator charging?

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.

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

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.

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

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.

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.

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

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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.

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.

[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....

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Here's the deal. IF the battery is fully charge, then yes - letting it sit for 3-4 days is no problem. If the car sits for 3-4 days, then is driven for 6 min to WalMart, stopped, then started again, and drive 6 min from WalMart to home, the battery is NOT at float full charge voltage. If this is the common duty cycle, and the driver is using the AC on full, radio, maybe the lights, then the battery is never able to get to a full charge state. So, pay attention to what I write, because you didn't get this far: "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 ." Bolded just for you pedants.

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LMAO, I payed attention, I just think you are incorrect....

Dave's not home man...

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One of the classic comedy albums of all time! For those of you who remember �The Big Bamboo� from Cheech and Chong.

All 996’s are hard on batteries. Get an agm battery, and one of those sweet novo genius battery tenders. Really solved a lot of problems for me!

Does it start fine at home, then won't start when you come out from shopping? And your battery is new or checks out ok? Only has problems after driving? Check your Y cable connecting starter and alternator. $75 or so. Does that sound like what happens to your car?

I had the same problem in my 2003 cab Replacing the Y-cable fixed it.

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"Who is it? It's Dave, man. Hurry up I got the stuff! Who? It's Dave! Dave? Dave? Dave's not here!" Funny thing is I can quote entire routines but sometimes have trouble remembering my own phone number! "Seen the damage done..." True! True! It was fun none the less...I think...!

I've told this story before, but I'll do it one more time for posterity and for Davey the 75 year old first time Porsche owner! That's keeping the dream alive!!! Anyway... when I bought my car (in Chicago) the battery was for all intents and purposes dead - the car started with a jump, but the battery wouldn't hold charge (Interstate proper large spec. battery - don't know the model off hand) even though the volt meter showed it was charging. I took the car around the corner to the local "AutoZone" (I don't remember the actual store, but it wasn't O'Reily's - though I tried them too), they put it on their tester and they claimed they could charge it - "come back in two hrs"... When we got back, they said the battery wouldn't hold a charge, was shot and that they'd be glad to sell me another. Well, the battery was less than a year old and was still under warranty so I wasn't ready to give up on it yet - unfortunately, they couldn't honor the warranty because they didn't carry Interstate. Fortunately for me, I was planning on being in town for another two days so I had a little time. It just so happened Interstate had a factory distributor in a industrial park in the next town over, about 25 minutes away. I brought the battery directly to them to see if they'd honor the warranty. When I got there and showed them the battery, they said they would absolutely honor the warranty, BUT!... They'd have to try to "deep charge" the battery first to determine if it would actually hold a charge - he said it would take 8 to 12 hours on their special computerized system to fully discharge then charge and test the battery to see if it met factory specs. At this point (it was about 2:00 in the afternoon) it meant I'd have to leave the battery overnight and come back the following morning. If the battery turned out to be no good, they replace it free of charge. So, I called the following morning (Sat) around 10 am and they said they were just doing final testing, but everything looked good and I should come in around 11:00 to pick it up. I've got to admit, at this point I was sort of hoping that the battery was bad, and they'd just give me a new one... No such luck! The original was fine, took the charge and passed all cranking amp tests with flying colors! Oh boy, I've got to drive this thing almost a thousand miles tomorrow, and I'm hoping the battery doesn't die on me Fast forward 4.5 years, and I'm still using the same battery! It's never died on me, and it always cranks strong. The car sometimes sits for over a week and has never let me down. If I know it's going to sit for more than a week or two I'll bring it up to my garage (off site from my home) and put it on the battery tender. All this being said, it's really important that you lock it up when parked so it "goes to sleep" and reduces the power usage (alarm/system monitors) while the car isn't running.

Never had any problem leaving my car for weeks, unlocked. Always started right up.

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Oh yeah, forgot the Y cable fiasco. That is on the 'to-do' list for all 996s. Good catch.

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I swear, I can write stuff on this forum, and people just don't care. They 'know' what they know, and no one can tell them otherwise(not referring to you, of course - you did it right). Even people with letters behind their name, doesn't mean a thing. Sigh. Here's what Interstate knows: https://www.upsbatterycenter.com/med...stic_curve.jpg Take a look at where charge voltage(constant) crosses charge volume. At about 6 hours, of continuous charge, the battery is now at ~85% of it's rated volume(ampacity), but most would consider it 'fully charged'. It - just - is - not! Almost all vintage car batteries live in this 60-85% charge state, and will provide enough current for long enough to barely get the car started, and running. That's why the DD cars batteries last much longer than seldom driven, short duty cycle batteries. Also why I recommended a battery hydrometer. The chemistry of the battery never lies. If you had checked the battery when it wasn't starting the car, you would have found it to be almost dead reading on the hydrometer(red, maybe yellow ball floating, others not). People with trickle chargers rarely have this problem, but to expect a modern car battery with all the parasitic draws to maintain starting current, is madness, I say - utter madness!

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^^^ I hear ya Doc ^^^ ! Had I not experienced it first hand, I have to admit I'd probably be skeptical my self. In fact, the guy I spoke to, did a pretty good job of explaining that chart and their digitally controlled "deep cycle" charging system. In hindsight it's pretty obvious that he was confident that the proper charging of the battery would work - otherwise he would have just given me a new battery on the spot. And, yes - While I'm not as old as Davey, I remember the "old days" before "sealed batteries" when we could buy new electrolyte (battery/sulfuric acid) and just replenish our own batteries...I think the Insurance companies had something to do with the end of that practice...

Assuming battery, alternator, and Y cable are good, I would hunt for parasitic draws that exist while it sits. Does it have an aftermarket stereo system? If so, this may be the source of your problem. I did some experimenting with mine, and it appears there is a small, constant, draw from the immobilizer/central locking system. I installed a switch on the battery that I open if I plan on letting it sit for more than three days. There are some great YouTube videos on identifying parasitic current draw in the many electrical circuits by methodically narrowing them down with a volt meter until you find them.

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One can buy battery acid right on ebay or amazon: Amazon Amazon I've used it before to rejuvenate a battery. It's not rocket surgery. BTW, a lead/acid battery is never sealed. Although the top may be flush, there is always a vent somewhere. Usually the flat center flap can be peeled off what appears to be a 'sealed' lead/acid battery. They cannot be sealed because charging generates vapors that must be discharged or the battery will asplode. I've seen batteries asplode when the vent gets blocked. It is not fun. As a boy of 14, I worked at a tire/battery shop. We rejuvenated hundreds of used batteries. We also sold used tires, and recaps. My dad had a shop on Garnet Ave in Pacific Beach. I could surf in the morning, and change tires, and batts in the afternoon in summer. Remember recaps? Jeez, I'm old.

Oh boy.... Lots of information in this thread, and most of it is correct. But lots of it is no longer current. Today’s car batteries should never require anything to be added to them - they are either sealed (typically AGM) or supplied with enough electrolyte to last the life of the battery (maintenance free). AGM will perform better but has less tolerance for overcharging, undercharging and abuse in general. Also they only last if they are not mounted in the engine compartment (like our 996’s) or my BMW (in the trunk). But - if your charging system is working properly, a standard battery will work well, and will cost less than AGM. Battery tenders are great, especially with AGM batteries. Also the advice to drive the car is great too - car batteries are not designed to sit indefinitely on “float” and that will shorten the life somewhat. Daryll

I use "float" with a caveat that I didn't go into the storage charge, discharge, cycle, which is beyond the scope and rather detailed for a Porsche car forum. One can google the life cycle of batteries and how they operate. I say again, lead-acid batteries cannot be sealed. A battery on a proper charging system will have a absorption cycle, charge cycle, and a 'float' cycle. Now, we have entered the realm of battery esoterica, for which there is no escape. I"m getting off here, I've made my point, and the rest of y'all can disagree until full discharge is accomplished. I suppose to account for the even more pedantic, I should have used "smart" before "float". Or, "intelligent" maybe. To repeat, drive the car, drive it for a while, don't make short trips repeatedly and expect the battery to survive very long. adios <edit to add, for those who are into minutia, here is the manual for aircraft batteries, which are rather sensitive to absolute right and wrong methods. An aircraft battery is designed to survive in strange environments, must be as light as possible, and operate without any potential for fire/explosion. It is 65 pages long. Report back if one finds an inaccuracy in anything I've written: https://www.manualslib.com/manual/12...25.html#manual >

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Had the same issue - bought a Ctek maintainer then replaced the Y cable - fixed I have now just recently installed an Optima red top D34 with a YellowDog motorsports adaptor plate - quite happy with it. Year ago I had an Optima blue top that lasted more then 7 years and I didn't even charge it on a maintainer!

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^^ This is the problem with internet forums in general - lots of information, much of it right, much of it wrong, and much of it somewhere in between... Most people simply don't have the time to explain every detail regardless of their knowledge on any given subject, so things get boiled down/edited by the author and often misconstrued by the reader - then repeated, often exacerbating the misconstrued "facts"... It's a vicious cycle!!!

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Once you get your car fixed, these handy jump start batteries can relieve anxiety and never leave you stranded again. Or if you are stranded, can power your cell phone for a long long time: Amazon Amazon

Gee Davey...where'd you go???

@75 maybe I hope he's NOT six feet under There better....not so dark

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^^^ Uh... that's some dark humor Joe

This went from informative, to funny, to dark faster than expected. Stay gold Rennlist, stay gold....

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Davey's still missing though...

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Mine is a -94 993, it can sit five weeks without a problem but 993s from -95 and onwards with the remote controled alarm are notorious for draining batteries!

Davey still missing - maybe he was a TROLL !

At 75, he may have forgotten all about his first and last post on RL.

75 is the new 60! (The Japanese say once you hit 60 you're already senile )...

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Dang! No wonder I keep forgetting stuff. At least now I have the excuse