Car does not start and has random electronic reactions...

Hi all, I just tried to start my 996 after having a flat battery a week or so ago, I am again experiencing some problems. This time it is the following: After opening the car and turning the ignition key, it does not start but the windows start going up and down (as much as they do when opening the door), the lights go on but become weak when stepping on the brake, the voltmeter is below 10V and the gear lights switch from P to 4 and back. After a while the alarm suddenly went off... Do you think that is again "just" a flat battery or might I be facing a more difficult problem? Thanks a lot.

Almost sure to be the battery. The symptoms are typical.

Thanks Richard, I had a few times problem with the Battery but never had the moving up and down of the windows and the alarm going off...but well I guess I call my friends from the breakdown service to get to my garage and get a new battery fitted. Or does it maybe make sense to get a jump start battery? Probably I cannot buy any as they might not be powerful enough. What are the characteristics the jump start battery should have to work with a 996? Thanks a lot again

All the control modules hate low voltage, and do all sorts of weird things when the battery gets low. You didn't mention the spoiler, but they also start having a mind of their own. I've never had much success with the self-contained jumper packs, as the batteries never seem to have much grunt. I have a 75Ah Bosch battery I use when necessary. If you jump the battery, use the terminals in the engine compartment. The positive terminal is under a black plastic cover, and the ground is the stud securing the back of the airbox. Now that I am alternating cars, I always leave a battery connditioner on the one I'm not using, and if you leave the car more than 3-4 days, I suggest you get one. I got a Ctek XS3600 on eBay for around £30, and it solved the problem completely.

Thanks, I think that makes sense. But do you mean leaving the car for 3-4 days or do you mean 3-4 weeks? As I used to leave it for 2-3 weeks before and never had any issues, so that I am wondering now if I should get a new battery.

If yours lasts 2-3 weeks, you are doing well. If I leave mine for a couple of weeks, the battery struggles. Mine has a tracker fitted, and I think it causes the additional drain. (Note to self: must find it and disconnect). Normally, the car consumes about 40mA when locked, so for every 4 days will drop the battery by around 4 amps. I reckon mine must be more than double that, so after a couple of weeks it is probably down around 35-40 amps. If I leave the conditioner connected, it isn't an issue. Most people who don't use the car daily use a conditioner. It helps prolong the battery life too.

Surely you mean 160mA if its left for 4 days? When i went on holiday last month the car was fine after being stood in the garage for a week started first time, the real challenge for me is that next year im getting married and our honeymoon will be for 20 days so i'll see if it lasts that long[ ].

No, I mean 4 amps. 4 days (~ 100 hours) @ 40mA. As I said, I'm sure mine uses at least twice the norm, because of the tracker, which drops the battery enough to make it struggle after a couple of weeks.

Yep me too. Never had a car that needs to be on a life line like this one.

Sorry forgot to mention, A good Jump pack http://www.powervamp.com/product_result.asp?ProdDivision=5&Subcat=12v%20Jump%20Starters I have about 15 of these at work they last years and have a big punch.

School boy error, i thought you meant 4 milliamps a day[ ].

Thanks everyone, it turned out to be just a flat battery indeed. Now I think I will explore the idea of a second battery and or just the jump starter. Another idea would be to disconnect the battery but as I don't park the car in a garage I don't think it is a great idea as I could not close the bonnet...