Anker tweeted this code earlier and I thought it might be of some use to someone! https://twitter.com/AnkerOfficial/status/552113568746078208
I don't have this particular model but I have a couple of older batteries and they are brilliant.
Add the Anker Astro E1 5200mAh External Battery with PowerIQ™ Technology to your basket and enter the code ASTROONE at checkout to get £4 off.
(£15.99 - £4 coupon (ASTROONE) = £11.99)
The following is taken directly from Amazon's product description section: PowerIQTM Detects your device. Delivers the fastest charge.
Exclusive to Anker, PowerIQ amp-adjustment technology intelligently identifies your device to deliver its fastest possible charge.
Charge your Apple or Android smartphone one to two times while on the move. You can even charge an iPad mini to about 80%!
This thing is remarkably small. About the same size as a small candy bar, you simply will not find a more portable powerpack.
We use only premium battery cells, together with the most advanced materials and cutting-edge technology, to ensure complete safety.