Astra
As your in the UK this is the one I use
http://www.powerbee.co.uk/Solar-Phon...rger/p-84-383/
Excellent charger, 3500mah battery, power meter and connectors for all my readers/phone/ds etc - the charging tips plug into a usb port on the charger so as long as you have a usb cable it will charge anything. (The micro usb doesn't have any data connectors so it will even charge the sony x50 readers)
I just leave it angled toward the window and your fine in the summer (Bit grim in the winter, but if you need it just as a spare battery it will charge from a USB port as well)
I've got a few solar chargers and this is by far the best
Regards
MikeB