Cottonpickers Solar Battery UPS Case!
I like it because it will allow you to run the Pi off power and immediately cut over to batteries when theres a power cut. Whilst you use the Pi it charges the batteries back up. The solar panel is included to run the pi for extended periods in the sun and also to charge the cells ecologically
Just pop in 4xnimh batteries and your Pi and you are good to go.
Charging rate is a nice 70ma to trickle charge and keep them topped up.
The panel is over a watt and over 250ma so it can help the Pi run for extended periods in the sun (over 6 hours for the B+)