That's some small differemce in the hardware. Nothing you can do about it.
But why not charge it with a mains adapter?
I have one Iphone 4s and when i charge this phone on laptop (Dell - Windows xp) the battery stays for a long time. But when i charge this phone on another laptop (Dell - Windows 7) the battery stay only for 3, 4 hours, and you have to charge again.