maek sure you had the right type of alternator installed. It might not be putting out enuf amperage for you or it might just have a bad connection on it. What you should do is take a multimeter and measure the voltage accross your battery while the car is on and at idle and then also while the car is at like 3k rpm.

if it's just not putting enuf power out, take it back and tell them to clean the connects on the alternator terminals or to give u one that puts out what it should.

gug