This is an interesting Kickstarter project that looks like it will be funded by September 11th and shipped by January.

The Estream is a small generator that converts moving water to charge an internal 6,400mAh battery and be able to power and charge usb connected devices.

It produces 2.5 to 5 watts of energy and can  fully charge the 6,400mAh battery in 4.5 hours.  After that it can power your devices twice as fast as a regular outlet.

http://mikepotterhere.com/wp-content/uploads/2016/08/c3039e464c95318bccebe4fc38790eb9_original.jpg

Do you think this would be useful to you?  The first supporters can get it for $180.

https://ksr-ugc.imgix.net/assets/013/303/424/b1cf7b2799f2095e72458fcad9b6230b_original.jpg?w=680&fit=max&v=1470600225&auto=format&q=92&s=d56e2f52fbe0755c45e1913f399a3659

Source: https://www.kickstarter.com/projects/hyerinster/estream-a-portable-water-power-generator-fits-into