The bigger backpacks have a capacity to provide 14.7 watts of power from a day’s worth of being under sunlight. And the smaller models have the capacity to give you 4 watts of power which translates to one and a half hours of cell use, or three hours of iPod use. The internal custom battery also comes with an adapter which allows you to charge the internal battery as you sit in your chair working at the office so you are always charged up for the commute home. They come in 5 types which cost anything from $ 600.00 dollars for the Laptop carrying bag two just over $ 220.00.
Mind you people who might be interested in the said products, they are quite tough and have been designed to be tough but be sure to remember that they contain electronic parts and an internal battery that may cause harm if not treated properly. The solar panels can break, the battery can leak (say you left your backpack in the car which was parked under the sun when you left for a vacation for a week or so which can literally melt plastic and the many other sensitive components that make up the said devices) and so on and so forth so treat the said bags as if they were any electronic device (“WITH CARE!”). Read all the warnings and precautions so you do not get surprises such as a leaking battery that you accidentally cracked open when you stood over the bag releasing toxic chemicals that can burn your eyes and skin.