The Battery should not affect the USB power, but it's curious about the 2.1 Amp port on the Hub.
Personally, I don't think the old USB standard was ever meant to drive a Bus powered drive, startup draw of a Hard Drive is really hoping for a lot from 500 mA.
Even their own Power Adapters are at least 1.5 Amps!
PS. I'm very glad I could help.