Found a cheap USB charging solution, YMMV

[Joshua]

Found a retracting USB to Pin/Barrel connector at Dollar Tree that fits and charges the S7. Keep in mind it may take 6-8 hours to charge over USB. Hope this helps you guys out.

 

[Carbira1]

That's cool. What's the quality of the cord?

 

[Joshua]

Very thin, but it is one of those retracting style cables and its only a buck, so you can buy several incase they break.

 

[WXMAN]

Is there any concern about getting incorrect voltage with this method?

 

[pa49]

Is there any concern about getting incorrect voltage with this method?

No need to worry about voltage!
All USB "ports" should give a nominal 5v.
Just make sure the cable is fully unwound a check on heat build up from the current shortly after plugging in.
I'm going to see if I can track one of these down today and give it a test as well as the Duracell "combo" charger mention in other posts.