Yeesh,

I'm sorry for introducing a mini-debate on this.

Your alternator is NOT designed to charge a dead batter, as Zoanas said.

You WILL damage an alternator this way.

In fact, the alternator will not keep your battery charged if you constantly run heater blowers or AC, headlights, stereo, etc all at the same time. And in extreme heat or cold, the battery may not hold on to a full charge.

It is a good idea to top up the charge on your battery with a maintenance charger, or trickle charger at least once a month. This will make your car's electronics happier, and your battery last longer.

Those who will disagree, do whatever. It's your car and your wallet.

I drive with headlights on (legal requirement on many roads in Italy) and either heating or aircon on and almost always stereo on with my d.d. 3.2. Assuming the alternator is not keeping the battery fully charged how long would you expect the battery to last. I also see temperatures of up to 38°C in summer and -20°C in winter. battery was fitted 2 I/2 60K km ago. Has not been charged.

I agree a trickle charger is better for a car not in daily use and I agree that jump starting is not good for our electronics but needs must when the devil drives. I have seen both Porsche and Ferrari dealers as well as the AA and RAC in the UK,called out to cars with flat batteries and notwithstanding the risks they jump started.

Gee, I'm glad I don't know all the damage I'm doing to my alternator and battery, because apparently they don't know either. So we're all happy.

Post scriptum.
my other 3.2 is a bit of a garage queen. When not used regularly ( at least once a month) her battery often needs a charge if I haven't disconnected it. Easy when I'm in my own garage.

an alternator is not designed to recharge a DEAD batt. it is there to put back what was used during the start up and run the electrics in the car. unless u have 2 sets of 100 watt bulbs, a 1000 watt stereo system. the stock alt will run what is stock to the car plus a few extras with no problem. i had an interstate batt in my 9114-6 that had a hole in it and the cell was dry. i drove it almost a year like that.....til i left the lights on.

if your batt is going dead while the car sits for a month, you may have a current draw. disconnect the neg terminal and clip a test light to the cable, then touch it to the batt post, if it lights, you have something drawing current.

i did electrical work on cars for a little while. we would even get ones from the dealers that they couldnt fix.

Ssssh--don't tell my alternator. It thinks it's supposed to freshen up the battery rat quick no matter how I kill it.

Oh, and did you know that turning the steering wheel while the car isn't moving will grind holes in the bottoms of your front tires and cause the steering rack to crumble?

Absolutely right! It's caused by the bastard alarm and anti-theft system my insurance company forced on me. A friend with a 996 has an even more sophisticated version that only manages a week! My gf's Boxster has a different make and sat for almost three months without problem.

alarms were always a big problem. especially if they butchered the wiring putting it in, not to mention coins in the rear ciggerette lighters (kids). glove boxe and hood/ trunk lights

So every car that AAA comes out and jump starts has a damaged alternator? Are they liable?

Next time my regulator goes out should I leave the lights on and have AAA jump it and have them buy me a new alternator?

I wonder why they continue to do this?

if the batt is dead, recharge it with a charger. if you jump it and let the alt do it, it will recharge it, IF, it is a good batt, BUT you will put a big strain on the alt. and most likely you will get away with it. im not saying do or dont. im sure everyone out there has at one time or another jumped their car just to get home.
jumping is not so much dangerous to the alt as it is to the computer, although i have never actually heard of either one going bad from jumping.
if you leave the lights on and drain the batt, if it is a good batt it will "recharge" itself some what after a while, so, if you do ever leave the lights, wait a while before starting, you may only get one shot at it. (im sure im going to hear it for saying that)

"bad" as in "bad battery" is a relative term. Easily cured for the less bad batteries by leaving it on a charger. Not cured at all, no matter how much charging is done on a really "bad" battery.

not too terribly expensive but a pain in the butt to deal with a bad battery.

"bad" as in "bad alternator" is an absolute term. no matter what, you're going to have an expensive repair. It's not convenient either. Why would you deal with a "bad" battery in a way that leads to a bad alternator? Never mind, I don't want to upset any delicate egos.....I'll just ponder that one myself.

So why have I never had a bad alternator? Or a bad battery, for that matter? You people spend way too much time worrying about things that never happen. And in my case, as I said earlier, "never" is since 1952. If I can make it through another 15 years, maybe--just maybe--I've beaten the crybaby odds.

Wow, are you guys seriously arguing that using the alternator to recharge the battery will not harm anything? The charging system in a car is, and has been pretty simple for a long time. There is no debate about the purpose of the alternator is there? Is there debate about how the battery operates? About how current and voltage work? What about diodes? Have they changed recently?

Just because "you've done it for the last 20 years", it doesn't change the fact that the charging system isn't designed for that. You can get away with it forever, theoretically, but to argue that it isn't doing any damage is simply wrong. You can argue that the damage caused is acceptable to you, and that you haven't had any problems as a result of your misuse of the system, but there is no questioning the design.

Glad I spotted this thread. News to me. Being a complete ignorant when it comes to car electrics I am afraid I had no idea the alternator were susceptible to damage jump starting the car. Like S.W. I have done it for decades and 'recharching' the battery by driving.

I wonder how many alternators I have fried without noticing it.

I really need to read up on car electrics..

OK. so I got home tonight and was prepared to remove battery to charge it. noticed that the negative cable was really quite loose. SO I thought perhaps the loose cableis my problem. I proceeded to jump start it again and got it running. but by then my friend had come over with his multimeter. As the car was idling I disconnected the jumper cables and thought I'd see how long it ran. While doing this My friend put on the multimeter and we watched the numbers dive from 13 to 4 with the jumper cables off and at 4 the car shut off.

The battery is now on the charger for an overnight charge.

My questions are:

Where is the voltage regulator located on this (1979 911 SC)
How do I check that with a meter?
How best to check the alternator with a meter?
How do you remove the ALternator in case thats what I need to do??

Could the loose negative cable on the battery have created these problems if the alt or regulator is bad?

I have never seen anything that says charging a completely discharged battery (Vbatt <12.2 volts) will in any way harm a typical automobile alternator.

Perhaps you could steer us to some of this alternator design info (data sheet) that you have knowledge of that states the design limits. Or is this just anecdotal evidence also.

Your battery went from 13 volts to 4 in a matter of seconds? The battery does not sound healthy

Google it yourself. Facts are facts.

I had batteries with internal shorts which sounds like your problem. It appears to have 12 volts one minute, then it drains down to nothing. Shock it with a battery charger, and it goes up to 12 volts again. Problem as I understand it is debri/corrosion shorting the plates. Toss the battery.

I have... came up with nothing.

You are the one that professes to have hard facts. Please share.