easy guess ....
1. i got iphone 4 32 GB , after fill up 20 GB music/video/photo in my iphone get slow and drain battery , so i remove them all , it run more smooth with out crash screen ,
2 . 64 GB is alot , people will sync around 50 GB all stuff in , apple have to make battery could handle it same like 16 GB , so let say ,
16 GB drain 2 hour
64 must drain the same 2 hour
which mean , if we remove all that stuff 50 GB out , then battery more improve than 16 GB
i know is hard to believe , but most of guy in this forum got 64 gb get better battery result like 5-7 hour after charger
No.