Hi Sarikan,
Have you looked at Solargorilla & Powergorilla from
www.powertraveller.com ? Sounds like you are doing a lot of reading as I do with medical books etc.
These 2 devices can charge anything from Macbook Pro (with an adaptor), laptops, cell phones, anything at all, several times over (Powergorilla has huge backup battery).
However, they are quite expensive, I am thinking of getting Solar or Powergorilla or both rather than run out of juice at inconvenient times.
Pity DR's battery life is so poor even with 1.02 update, maybe 1.5 firmware will make it better. I will hold off till January before going the Gorilla way.