Charging Issues..Please Help
 

Well, I started noticing that if I dont start my car for like a week, when I get in it, the battery is dead. Not completely dead, but with just enough juice that it makes the starter click: "click, click click", but wont turn the motor over. The battery is a yellow top optima bought brand new a little over a year ago. The car has a stock alternator, with an underdrive pulley. I started noticing that while driving, my amp guage was getting really low like 10-11 volts. I took the car to have the alternator tested, and they said both the alternator and battery were fine. I went ahead and ordered the overdrive pulley for the alternator, which is suppose to remedy the low voltage while driving. How should I go about checking what is staying on and draining the battery? Thanks Gang!