Interesting you should bring this up. Was researching the product just last week. First, I'm not even sure you can purchase same at this time. Secondly, if battery life is an issue just bring another battery. Thirdly, I'd make darned sure the connector(s) are really compatable with your phone/what-ever.
Personally, I'd just run down a roll up solar cell pad if recharging is an issue.
An 'idea whose time has not come?'