Need specs. for a USB Pocket Hard Drive

I recently purchased a USB Pocket Hard Drive. As the device needs to utilise the full 500 mA that the USB port can supply it has a two A connectors, the second of which is to provide power only (ie. data is only transmitted through one connection).
Most computers that I use only have one available USB port or have a small B type connector sitting on the desk for use.
I am worried that I may lose data by not having the second (power only) plug.
I would like to build a battery pack that I can connect into the USB cable to compensate for the lack of a second plug.

Does anyone have any ideas about the construction of this battery pack?

If you would like me to attach some photos, or if my question does not make sence, please post a reply.

Thankyou

you should be fine with a battery pack with a 5v regulator (ie- 7805 or similar) hooked up to the power pins of the power-only part of the usb cable.

the only problem I see is that when a computer powers down, goes into standby, or hibernates, it turns off the USB ports. at best, you'd be wasting battery power running the hard drive with the computer off, at worst you may damage the USB port by holding the power at 5 volts when it is supposed to be off (you'd have to find out if the USB port power is floated, or pulled to ground, when it turns off) not to mention, you'd probably be powering other USB ports with your battery pack also depending on how you wired things up, so when the computer turns off it may drain your battery very quickly.

you could rig it up so that the battery pack is only turned on when 5v is detected on the primary (data) usb connector.