how to stem battery discharge

Does anyone have a "hack" on how to avoid battery discharge when the car is not being regularly? I'm reasonably new to the 996 and spent all last summer driving my '99 cab regularly; so I never had an issue. Now, this winter I noticed that the battery would discharge pretty fast (maybe a week). Even on my '01 coupe, the car will crank slowly if left for several days. I have installed master cut off switches, but these are a bit of a pain (radio codes/pre-sets, etc.) Both cars came with trickle chargers, however I don't have power to my storage shop. Both of the car's have new group 48 batteries. The charging system indicates 14 volts after starting. I haven't yet tried to measure the amount of load bleeding from the batteries when the car is turned off. I was wondering just what the main culprit usually is? Is it that the car's computer stays on to work the windows? The radio? The security system? Does the key's RF signal have to be a certain distance before the car's computer will completely shut down?

Locking helps, too. Puts the car in "sleep mode" after about 5 days.

Yes, locking it does help. How old is your battery? Not that much you can do for cars that aren't driven much and like you said, no power to the garage. Solar panel charger? A new battery that has a born-on manufacture date this is 3 months old or newer might be just enough to get you over the edge and have the car sit for a week or more without much trouble. I've let me 996 sit for over a week and it's fine. I have a new battery.

The battery is shot within a week? You should find the excessive draw by troubleshooting. My 996's with several year old batteries go for a month or so at a time and will start up with no issues. But I've taken the time to address current draw issues.

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^This. Your battery with car locked should last at least one if not two months.

My observations: German cars like a nice, beefy, fully-charged battery or all manner of weirdness happens. They all discharge their batteries in stasis. They don't like to sit around. So...drive your car more often, put it on a battery tender or disconnect it if you're not using it. Replace the battery proactively every couple years. Oh, and 911s crank slow compared to just about everything else that doesn't have a propeller. If it starts consistently, it might be normal 911 slow cranking.

Locking really only helps with "Short Term" discharge. Locked or unlocked the car will go to "Nap Mode" within a few hours, or completely in "Sleep Mode" in 5 days requiring manual unlocking. You really need some type of maintainer.

1) Make sure you have good/clean grounds and your charging system works properly 2) Start with a fully �deep charged� battery 3) lock the car every time you park it 4) If you�re going to leave it for more than a week, put it on a battery tender.

No power at all .. not even a light in the shed? You could easily tap into that.. otherwise the solar power suggestion seemed good.

Find your emergency frunk or engine cover release cable (better yet both) and route it/them to an accessible place before you are locked out by a dead battery.

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Should you still lock the 996 (put it to sleep) AND put it on the battery tender if leaving for more than a week?

I would say yes, mainly because if the car is locked and the battery completely dies, you will have one helluva time getting back into the car. Even locked there is still a draw on the battery. If the battery is fresh and fully charged, one week probably not a problem. However, why not play it out on the safe side and connect a battery tender so all you have to do is unlock and drive. And relocate that emergency release cable on the frunk into the tow hook plug so it is easily accessible. Just do it.

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Its what I do, and I haven�t had a battery problem in 3.5 years - this is on a battery that was technically �dead� when I got it (interstate - took it to one of their centers - before they would replace it under warantee they had to attemp to �deep charge it�. They did, and it�s been good ever since). I don�t necessarily put it on the battery tender every time it�s going to sit for more than a week. In fact it was at my house all last summer, and I never put it on the tender - sometimes I didn�t drive it for more than 10 days... no sweat, open with key and start right up...

Not sure if the type of battery makes a difference but I installed an AGM last summer, parked the car early Dec come late Feb the gauge was showing 12+v and it started right up.

My 04 C2 can sit for a month with no noticeable change in starting the car. With that said, I always use a trickle charger when expected to be parked longer than a week (this will extend the life of the battery). I would perform a parasitic draw test "google it" to see what may be drawing the battery down. Make sure the battery is fully charged and you wait a week before performing the test since some electrical components will continue to draw until they are put to sleep. In addition, as was mentioned above, re-locate both the frunk and engine hatch emergency release cables for easy access.

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Even if I have a �99? Don�t �99s have real key locks and manual cables that release the frunk and engine bay lids?

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Yes, I do believe this is correct. You can mechanically unlock the door for access. However, if the car is locked down and the battery dies completely, the electrical system and immobilizer may not have any juice to "unlock" the interior cable pulls next to the seat, meaning until you get 12V to either the frunk battery or engine bay jumper point, you may not be able to completely unlock the car. The interior cable pulls are locked when the car is locked. A trickle charger plugged into the cigarette lighter might work to get things unlocked, however, if the battery is dead it might take hours to get enough charge, and you might run the risk of a damaged or bad cell in the battery that prevents charging and then you are screwed.

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Ahh, I see now - of course you are right. I forgot about the locking mechanism itself. But when the driver door is closed, the door covers the hood and rear deck lid handles, so I forgot those still have locks to them, not just protected by the door. Is there a way to unlock the front trunk and open it even when the driver door is closed?

To the best of my knowledge...nope. Not only can one not pull the cable release when the door is shut, if the cable pulls are locked and the battery is dead, then you cannot do it either. Thus the recommendation to relocate the emergency frunk release cable to an easily accessible point.

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Ok, good to know. Perhaps this is why some folks opt to leave their car unlocked, but from a security/theft perspective, not a good idea to leave unlocked, even in a locked garage. Last question: does pulling the emergency realease a locked frunk?

I have had two 996s. Both displayed the exact same behavior. If you leave the car unlocked the battery will drain enough in 7 days or so that starting can be problematic. If you lock the car the car can sit for a month or more and still start easily. The car never shuts down the remote radio receiver while unlocked. It is obviously a substantial battery drain.

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Both the front and rear emergency release are connected directly to the latch mechanisms. No power needed.

Hi all figured I would offer my input as well. We are a new vendor, Antigravity Batteries to Rennlist and sell lithium batteries for motorsports vehicles. Lithium-Ion batteries tend to have a lower amp hour rating than lead acid, but much higher cranking ability than lead acid. So parasitic drain is an area we always look into diligently on the vehicles we have our batteries in. We have a 2106 GT 3 RS with our Battery in it..... And what I can tell you from my conversations with my Porsche Tech is that since 2005 Porsche has had a battery management system in the vehicles, and that battery management system would turn off certain areas of the vehicle and put them into sleep modes. But initially the battery management system was very broad and would turn off many systems all at once and put them to sleep. Whereas now it is much more refined and can actually put certain areas of the car to sleep to minimize the draw on the battery system earlier and more efficiently. Since 2014 the system has become extremely efficient and from the 2014 and recent models the parasitic draw is exceptionally low... In fact we have an 18 amp hour battery that weighs roughly 7 pounds and can last a month if not more in the GT 3 RS and other 991.1 models as well as Caymans and such. But as many of you had said the earlier models do have a significant parasitic drain if you don't make sure you lock the doors... The tech I spoke to believed that because the doors aren't locked the car puts itself into more of a ready mode thinking it will be driven soon so it never goes into the deeper status that it achieves when the car is locked. So that definitely could be an issue with the 996 as many of you have claimed Anyway I just figured I would also add that you do not want to have your key fob near the car or stored in the garage with the car. This may not apply to some older model years. But the key fob awakens some parts of the system of the car because the car is looking actively for key fob's in the vicinity. Last, if you ever put any aftermarket Bluetooth system, alarm system or any accessories those tend to have create dramatic draws on the battery. I have measured some Bluetooth systems that draw over 2 amps... And that is crazy actually because a correctly functioning Bluetooth device should be able to draw just milliamps... But many times these systems will be actively looking to connect to a Bluetooth device in the area so they stay active which the owner doesn't realize. The fact is if you're drawing down a 70 amp hour battery in a week that's pretty significant so you're definitely going to want to make sure you're locking the doors and as others have said tracking those parasitic draw's which you can do through the fuse panel and by using a typical and even cheap multi meter.... Rather than me explain how to hook up to check parasitic draw you can go on YouTube and search for how to check parasitic draw which is also called phantom draw and you will find YouTube videos that explain it quite well.

Thanks fpb11: Those ma numbers will be very helpful when trying to find the draw. Antigrav: It looks like I can no longer leave the car unlocked and the keys in the console... living in the country has it's perks! But apparently hard on the electronics.

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Sure does. In and around the city, stolen cars out of garages and streets, are no longer the preferred method for thieves. Modern vehicles are increasingly harder to steal without the proper keys. Therefore, car jackings, although risky, come with they keys in nearly every case, or at least, with the car already running. So the advice people are giving these days is to lock the car in the garage and keep the keys in a different place far from the vehicles.