Just as it says in the title - external battery pack/charger for my 3GS phone.

I'm looking for an external battery to help me through long flights and make sure I have some juice at the other end to make some calls and check my mails.

I don't want a case with battery, as I like my current case.

I would prefer a cable connection rather than a plug-in direct battery.

Ideally, I'm looking for 2+ charges for my phone from the external source.

And I would like to be able to get it in the UK.

Thanks in advance!