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PowerMonkey Extreme portable solar charger
While a portable power pack has a finite storage capacity, by tapping into the sun's infinite power supply you can charge your smartphones and tablets any time of day -- even when it is overcast.
The PowerMonkey Extreme is kitted with a massive 9000mAh capacity battery inside a durable shell. The unit is capable of recharging most 5V devices, including the iPhone. In turn, the battery is kept topped up by a clam-shell solar panel offering 3 Watt of output.
It features two output channels, one channel outputs 700mAh max (standard USB) and a 2.1 Amps port that support the iPad and other 5V tablet computers.
Image source: PowerTraveller.