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Discussion Starter · #1 ·
My car, a 530i, is parked in a garage for long periods, sometimes weeks. I have learned to expect to arrange a jump start on my return. The proximity alarm and key-radio draw current all the time, and it takes the battery right down.


Finally I purchased a jump starter, basically a 20 lb battery you can charge in the kitchen, then use to jump start the car.

This time, however, the car has been parked for an unusually long time. It acts as though it had no battery at all -- or as though the circuit had been deliberately opened. I was wondering if the alarm system, as it runs out of current, maybe shuts down the car deliberately, as part of its program to disable the car for would be car thieves?

It may also be that my key transmitter circuit, also long dis-used, has gone to sleep as well.

And what next? BMW suggested I have the car towed in, but I wonder if I have exhausted the alternatives.

Thank you for your insights.

Best, Michael
 

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Well, short of towing, you're going to need some kind of a battery to get things going in your car. It could be a new battery or the old one needs to get charged up.

I think it is your key that is now dead and I'm not sure how to charge it up. Can you hook in the jumper, insert the key, and just let it sit there for several minutes to see what happens? Move the key into postion 2 and see if anything changes over time.

Or, get a new battery installed...it could be cheaper than a tow and service by the dealer.
:dunno:

Interesting situation you have there.
 

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Discussion Starter · #3 ·
Anyone who parks and flies will come home to a non-starting BMW sooner or later. It is a silly situation. Badly thought out by BMW.

BMW's service manager suggested to me that their fix for this problem is a box (for sale at BMW service) which plugs into your wall socket and keeps the battery topped up while you are gone. This is nonsense. There is no place to plug in a battery tender at an airport. In fact there is no outlet near the assigned parking place in my apartment's garage.

I think there is a lockout somewhere in the system that has opened the battery circuit. There is just no tiny sign of life in it. Usually, for example, you would expect a tiny dim glow from the interior dome light. Nothing. I will put a VOM on the car to confirm this, but I am pretty sure it will see an open circuit.


I think the key must charge via an induction coil. There is only one contact path available, the key itself. This is one too few. So I can't just hook it up to a wall wort charger.

Couple of years ago, I had the BMW battery replaced. The guy who did the work was very careful to avoid simply disconnecting the old battery. He first wired a tiny battery in parallel with the big one, using the cigarette lighter for contact points. Then he went ahead and pulled the car's battery. He explained that he had to keep the systems memory alive. I guess it is RAM, not ROM.

Point being, by this reasoning , a really dead battery would cause memory loss.
 

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Discussion Starter · #4 ·
Conversation with service manager

Today I spoke with the service manager about these problem. In his view it is to be solved exactly as Agent 99 has suggested. The battery should be charged or replaced, the key will recharge from the column, and that's all there is to it.

There are no lockouts or sophisticated security shutdowns or system memory failures to worry about. It's just a dead battery, as per usual.

I asked what would happen if I were to disconnect the battery before leaving, and he said that I would only lose the clock and radio settings. Fair enough.

Okay. Thursday I will make another attempt to diy (dim). I really don't want to have the car towed. Makes dents, etc.

Thank you again for your help.
 

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Discussion Starter · #5 ·
mystery finally explained

When the car would not respond to a Jump Start unit, it appeared to me that the starter circuit had been opened somehow, possibly by the car's security system. No.

It turns out that the Jump Starter unit contains a microprocessor, and the chip was refusing to close the circuit within the Jump Starter.

Why in the heck, one might reasonably ask, would it do that?

This particular Jump Start unit is idiot proofed against a reverse polarity connection. You hook it up (red lead positive, black lead ground) and the unit checks your work by detecting the direction of current flow, presumeably with a little diode logic. If you connected the cables backwardly, the microprocessor will refuse to let the jump starter operate. But to make this decision, some current must flow from the discharged car battery. If the car battery is simply too weak to drive the logic circuit (mine was) the Jump Starter won't turn itself on.

I called the service station. The guy came over with a lower tech Jump Start unit and the car started immediately.

For your reference, the unit he used is called the Jump 'n Carry 660. I recommend it. The one I was using calls itself a "smart" jump starter.

Too smart by half.

Another Nice feature of the Jump 'n Carry -- not only does it actually work, it has a built in voltmeter, so you can read the performance of your charging circuit.
 

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You should be able to use your key to mechanically open the trunk and driver's door I believe.
 

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Ågent99 said:
You should be able to use your key to mechanically open the trunk and driver's door I believe.
I thought so too but this isn't the first time I've heard people mention not being able to manually unlock the car, so rather than wait and find out for myself I replaced my battery yesterday as preventive maintenance. The place said they've had an unusually large number of dead car batteries since the heat wave here started.
 

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Anyone who leaves their car for extended periods should seriously consider use of a "Battery Tender". They are cheap and effective. While one could spend $70 for the factory one, you can buy the exact same one (without the BMW label) for much less here:
http://snipurl.com/7cod You then only need to splice on a cigarette lighter adapter like this from your local Radio Scrap: http://snipurl.com/bkwr and you are "good to go"!

Yes, this may not be useable when left at the airport for extended periods, but very useful when left at home (and hey, apartment dwellers, ever heard of an extension cord? ;) )

This is the solution for all those "garage queens" out there! I have done this for my rarely ridden motorcycle, and now I don't have to replace the battery every couple years....heck I've been on the same one now for 5+ years.

I even use them on my 540 and Ferrari when I know I will not be driving them for a few days.

If this is just not at all possible or unacceptable to anyone who doesn't drive their car for extended periods, then just put battery replacement in as part of your normal services, say every three years. Long periods of non-use, which drain the battery down, really shorten the life of a typical "starting battery". For that situation, a "deep cycle" battery might be a better alternative, since they are specifically designed to be deep discharged without damage. Although I have no idea if there is a deep cycle battery that would even fit, and meet the electrical requirements.
 
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