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The car is a 2005 Toyota Corolla CE. Its engine is the 1ZZ-FE, a 1.8L straight four that runs on gas, not diesel.

The alternator is stock, and tests out just fine on the multimeter in both voltage and amperage. However the battery charge is very low. After trickle charging it overnight, and starting the engine on the battery booster, the car drives a short while, then the engine stops.

My hunch is a disconnect in the electrical system, like a corroded wire. However, I would like to know if it's possible for a bad battery to cause the engine to stop. My understanding is that the battery is used only for starting the engine, but that may be overly simplistic.

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You have to tell more about the car, what type of engine (diesel / petrol), even more precise information about the type of engine would be useful. For example in a old 1980's Mercedes-Benz diesel battery is not required to run, even my 1992 naturally aspirated diesel does not require electricity - battery is only used for starting. In more modern engines I am not sure, but it might need electricity to run. –  miernik Nov 27 '11 at 20:20
    
Good point. Although all Corollas have petrol fueled engines, afaik, I'll update the post with information on the Corolla's engine. –  fatcat1111 Nov 27 '11 at 23:25
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2 Answers

up vote 3 down vote accepted

Generally, the alternator provides enough power to run the car, even without a battery present.

If your car stops as soon as the battery is disconnected, then you have a problem in the charging circuit. If you're 100% certain that the alternator is good, then something else is preventing the power from getting to the electrical system.

If the charging system didn't provide enough energy to run the car, plus a bit extra, then your battery would never charge.

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On many modern cars, like 1ZZ-FE powered Toyotas, the battery is in series with the alternator, so a battery (or battery connection) problem can cause the system to not get power. Not sure why they do that nowadays, perhaps for the voltage smoothing effect the battery has? Older cars were in parallel. I remember push starting my Dad's old J-Body when it didn't even have a battery installed! :-) –  Brian Knoblauch Nov 28 '11 at 14:06
    
This is my understanding as well, but I thought that perhaps I might have an overly simplified understanding of the process. Thanks for confirming that it's correct. Offhand, do you know how much power it takes to keep the engine running once started? I mean, leaving off things like the headlights, stereo, etc., what does it take to keep the sparkplugs sparking, fuel pump pumping, etc. –  fatcat1111 Nov 28 '11 at 18:19
    
I do not know what typical power draw is, but if your car isn't overloaded with too many computers, it wouldn't be too bad. Fuel pump would be the worst. Ignition system is high voltage, but low current. I know that OBD-I cars could drive on battery/no alternator for 4 hours+ before running out of power. I suspect that newer cars have much less reserve. Battery size is similar and they're loaded up with all kinds of extra computers now. –  Brian Knoblauch Nov 28 '11 at 20:37
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A modern Toyota will stop the engine when the battery is bad, it's a safeguard. Replacing the battery should fix the problem.

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Good to know! Out of curiosity, what is being safeguarded here, what is cutting the engine (is it the ignition timing circuit?), and how does cutting the engine safeguard whatever it is? THANKS! –  fatcat1111 Nov 28 '11 at 17:53
    
Do you have any documentation on this? I am not saying it's not the case, I am just not familiar with how or why they would do this. What does it safeguard against? Seems like it would be more of a problem if you had a bad battery. Instead of being able to jump the car off and drive it to the parts store for a battery, I either get it towed or take another vehicle. –  Larry Nov 28 '11 at 21:33
    
Is it drive-by-wire? That could be one reason, or something similar to the reason. If the carputer's turned off, it can't control the gas flow and stuff, right? –  Ricket Dec 14 '11 at 16:52
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