Battery test by gsmarena for Xperia p
Sony Xperia P battery life gets tested, 1305mAh found lacking by WhiteMagic screen - GSMArena Blog
Xperia p has USB on the go support
see the spec
Sony Xperia P - Full phone specifications
so it can support USB drives, but u need usb on the go cable for this [I don't whether it comes with the box or not]
Review for u as well
Sony Xperia P review: a solid, middle-sized smartphone waiting for Android 4.0 -- Engadget
My suggestion is increase the budget a bit and go for Samsung Galaxy S2