Tryna to diagnose my issue with my battery:

Ok starters its a new battery i got from the auto parts store 2 days ago because my battery died on me coming home so i replaced that i even replaced the altenator and it checks out fine the alt is a 99+ altenator do i need the 99+ plug/harness for that alt? Could it be a bad fuse? Checked my grounds even cleaned them but still battery drain im reading 11.4 on the volts and it goes down through time...any ideas? Could my rewire to my fuel pump cause this? Any suggestions? Thanks!

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