Unless they changed the rules a mobile device powered by battery is covered by a users own licence no matter location. As soon as you plug the device into the mains its no longer covered. Rather stupidly that means a friend can watch iPlayer in your unlicensed home using your Wi Fi and your IP as long as they dont charge there mobile. Although surly it looks to be impossible for the BBC to know if the mobile was being charged or not.
The entire charge rule is stupid. Mobile phone in car fine, plug your mobile into the USB to charge as you drive and no longer licensed technically. (Based on reading the rules over 5 years ago, I am assuming no changes)