alright so my car dies alot no a days. like ill go to bed and then wake up in the morning and go and start my car and its dead. it keeps doing it. and i was wandering how you can tell if its the battery or the altanator. im just assuming thats the problem. one of the two anyways
if it were me; i would replace the battery because that is almost always the problem and the battery is much cheaper and easier to replace. if you want to be sure, go to a dealership and have them load-test your starting system, charging system, and battery(they almost always only charge 0.5hours labor) and they will tell what is wrong/ok. on the load test, any battery showing less than 300CCA will start seeing difficulty starting. if you do go to a dealership and they tell you your battery is bad, just buy one from autozone, much much much cheaper. good luck!
also, and FIRSTLY; make sure all of your doors are fully closed at night and that your dome light doesnt stay on all night...also if you have any aftermarket accesories in the car that may be drawing power overnight, try disconnecting them for a night
A simple test is to just check the battery with a voltmeter. Black wire to neg, red wire to pos. With the car not running, the battery should read around 12.3 volts. With the car running, if the alternator is working, it will read around 14.4 volts. This is just a quick test admittedly, but it will point you in the right direction. If you test it and your alternator is working, more then likely it's in your battery. Just be sure to check your terminals as well, make sure they're not so corroded that they won't allow the alternator to charge even a good battery. And also, if your battery has filler caps, make sure the water level is correct. Even so-called "maintanance-free" batterys that have the caps need to be checked occassionally.
I'd do exactly what they said above, just have both parts checked. Sounds like a battery since it doesn't die while driving. That is a dead give away that its not the alternator. My alternator went and i literally watched the voltmeter drop as I was driving home. Scary thought since that road was 50 mph. And if it turns out to be the alternator (by some small chance) save yourself the money and do it yourself. Took me all of 30 minutes and basic tools. Good luck
Mike
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A simple test is to just check the battery with a voltmeter. Black wire to neg, red wire to pos. With the car not running, the battery should read around 12.3 volts. With the car running, if the alternator is working, it will read around 14.4 volts. This is just a quick test admittedly, but it will point you in the right direction. If you test it and your alternator is working, more then likely it's in your battery. Just be sure to check your terminals as well, make sure they're not so corroded that they won't allow the alternator to charge even a good battery. And also, if your battery has filler caps, make sure the water level is correct. Even so-called "maintanance-free" batterys that have the caps need to be checked occassionally.
its not just the voltage that is needed to start a car.
voltage is just the pressure that moves amperage; amperage starts the car.
you can have a battery with normal voltage (12-13 volts), and still not start the car due to a low CCA. a battery rated at 500CCA that tests at 100CCA will not start your car. the CCA rating(Cold Cranking Amps) are more important than voltage when diagnosing a battery.
typically, w/engine running, battery voltage will read 13-14 volts, w/engine off, battery voltage will read 11-13 volts
average CCA ratings on our size batteries are between 500-600 CCA, you need at least 300CCA to reliably start your car.
i have thesame problem and it was a short cut with my custom alarm but now my car don't start if i leave it for 3 days and sometimes it was the starter. try it next time turn your headlights without turning your car if the turn on then your starter is wrong hope this helps
I'd do exactly what they said above, just have both parts checked. Sounds like a battery since it doesn't die while driving. That is a dead give away that its not the alternator. My alternator went and i literally watched the voltmeter drop as I was driving home. Scary thought since that road was 50 mph. And if it turns out to be the alternator (by some small chance) save yourself the money and do it yourself. Took me all of 30 minutes and basic tools. Good luck
Mike
Yeah definitely change it yourself if it is the alternator. I had the same problem as Mike and it took me maybe 30 minutes and all you need is a socket wrench and a screw driver. Very easy repair!
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2008 Torch Red GT, Borla Stinger S-Type Catback exhaust, LED Tail Lights.
2003 Sonic Blue V6, 8" Shorty antenna, Smoked Headlights, GT fog lights, Sequential tail lights, Cobra IRS
alternator or battery 
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