Everynight my car runs out of battery power and needs a boost. Also, there is quite a bit of dimming of headlights/interior lights when idling vs revving the car. My friend has a feeling that it may be the Unorthodox racing underdrive pulley that the car has.

Since I've just picked up the car I don't know if it's the pulley that causes the problem or not. Please help.

 

At idle, the alternator doesn't have enough power to charge the battery, but it does have enough to keep it steady. Are you runny a system or anything? The dimming of the lights are common. Also do idle for a long time?