Kickstarter idea; free to a good home
How about hiding a smartphone battery charger in a belt; as in the thing that holds up your pants.
You can get these flexible lithium polymer batteries and there would be no need for the belt to be any thicker than usual.
offshore westerly 
http://thenextweb.com/gadgets/2014/11/19/belt-charges-smartphone-keeps-trousers-time/
On Thu, Dec 11, 2014 at 6:08 PM, offshore westerly wrote:
> mxx1 posted: “How about hiding a smartphone battery charger in a belt; > as in the thing that holds up your pants. You can get these flexible > lithium polymer batteries and there would be no need for the belt to be any > thicker than usual. “