Can anyone recommend a portable battery charger?

I travel for almost the entire day three days a week, for work and university. I take my Surface and wall chargers with me, but I need something more convenient and mobile for my 8X.

HTC offer a 6000Mah solution at around £45, but I'm looking for something a little cheaper, as there are hordes of chargers on the internet, starting from £5.

I only need one additional full charge, so something around 2200Mah should be more than sufficient. The more the better though, especially if it's a bargin.

I've already tried this: and it didn't work.

I assumed that "Output: DC 5V/1000mA; Intput: DC 5V/1000mA" would be compatable, clearly not. This also didn't work for the Lumia 800, and Lumia 710 either. But did work in an iPod Touch.

Can anyone help? I'm pretty desperate? Budget is preferably £9-£30 (as long as it's a good quality device, and not going to harm my internal battery in anyway - it also needs to be 'sleek' or slightly attractive.

Thanks guys?