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This isn't for my 2k1 it's for my 92 civic hatch. My battery light has been on for about a day so I check it out with a battery tester everything seemed fine no loss of power when tested. So tonight I go to leave my friends house and the lights start dimming, so I turn them off and let the car run for about 5 minutes get back in and turn the lights on and the car stops. I boost it with my friends car drive it about 500 feet and it dies again. Would this be the battery or would it be the alternator how can I tell the difference which one is faulty?

 
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to me it will sound like the alternator, because you said your battery is good, so its the alternator,

 
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If it is a battery problem the car will not start, if the engine is not running the lights will dim and the stereo will turn off. The battery is only in use to start the car and when the engine is not running. The alternator is in use only when the engine is running. So I think you have a problem with our alternator and if your battery is old it will not hold any charge.

 
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Yeah, and the battery light comes on when there's a charging system problem, not just dead battery. Just get the alternator tested to see if it's putting out the normal voltage.

 
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Alright thanks guys. I'll check it out.

 
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Thats your alternator dude

 
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Another way to find out would be: Start your car by boosting/ or it turns on. To see if it's the battery or alternator, carefully disconnect the positive terminal. If the engine turns off then that means that the car is running off of the battery, so the alternator is shot. But if it still runs that means that the car is running off the alternator which in turn means that the alternator is shot.

Hope that helps ya out. But from what everyone is saying, it's probably the alternator.

 
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I've heard that you can only do that on older cars....doing that to new cars can damage your ecu. I dont know if its true or not, I've just always avoided it.