my car starts up fine in the day, but when I have to use my head lights it becomes a problem. It will start at night then ill drive it around with the lights on every things normal. after I turn it off and come back to it I would say 2 or 4 hours it wouldn’t start. it turns over about 4 or 5 times strong then really becomes sluggish like the battery is almost dead so I try turning the key again and same thing 4 or 5 turn overs then sluggish. so I just let it sit over night about 8 hours and try to start it and it starts right up I don’t get it. I had my battery tested and its a good battery, could it be my alternator? (and its not a fuel problem)

 

Have alternator tested - any parts store does it for free in the car.