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For some reason my mind is blank and I cant remeber this. My girlfriends, roommate has a battery the terminals are loose on, I know that if she doesnt get it tightened the battery will go dead cause the alternator cant charge it blah, blah, blah. Alright i know on the old cars w/o ecu all that I know you can crank them and chunk the battery cause the alternator runs the car. Ok so my question is this can you do this on the new cars?

 
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Someone correct me If I'm wrong

But I believe that the battery and the alternator are more interconnected. The main draw on the alt is to charge the battery. I'm not sure of the porportions of draw from the battery compared to the alt of electrical devices in the car. But I believe many components run off the battery.

 
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See thats what I was thinking I thought I heard somewhere that in the new cars you CANT just remove the battery once cranked. Because the car will still go dead. Am I correct??????

 
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The battery is an integral part of the electronics system of a car.

Some cars with very high output alternators can run without a battery, which is why NHRA mandates a battery AND alternator kill switch.

Some cars, such as sprint and top fuel cars, run what is known as a magneto, which makes its own power to run the ignition system, and needs neither alternator or battery.

 
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Yeah our old ski supreme boat had a 351 ford in it that ran off a magneto. So my question is though that if the battery is dead the car cannot run just off the alternator?

 
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If the battery is dead to the point of no charge at all, then most likely the car will not run on alternator alone. But if the battery has a partial charge, just not enough to start the car, then it will run.

 
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yeah.. if you start the car and unhook the battery it will sputter and die . .

Might take a couple minutes though .

 
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I dont think its safe to do this anymore with modern cars that have computers in them. On older cars you could disconnect the battery to see if the Altenator is bad, but on newer cars its supposedly bad for the electrical/computer system.

 
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Yeah thats what I was thinking I just couldnt remember for sure thanks guys,
Realitycheck

 
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Yes you can, but I don't see why you would. The alternator will supply the electricity to run everything. When the car is running the battery is a load on the alternator and the alternator is the source of eletricity. When the car is off, the battery is the source and all the load will be on the battery.

 
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Actually, the modern car uses the battery not only for its storage power, but its use as capacitance, meaning it helps to filter out noise and voltage spikes that may damage electronic circuits.