Altenators and batteries

I have replaced my alternator,the belt and the battery on my 96 Maxima but something is draining the power.What could it be

Could be any one of fifty or more things. Someone needs to start testing individual circuits to see where the drain is. This is a time-consuming and potentially expensive process, but it’s the only way to figure out what’s draining the battery.

Check all the simple things first. Make sure no lights are left on accidentally (trunk, glove box, etc), and that the cooling fan doesn’t keep running all the time.

Automatic switches on hood and trunk lights, any of dozens of relays, any of dozens of diodes and transistors, just to get started. Search this site. One of the regular posters recently made a very coherent step-by-step explanation of finding such problems. Such a task is for the determined and patient… Or lucky.