I carry around 20 KWh* of unused, unwanted energy. Why can't a wearable tap into that and stay charged forever as well as improving my health and looks? We could even incorporate a USB port and I could charge all my devices from my abundant energy reserves**.
* 2 kg fat * 35KJ/gram / 3600 (secs->hours)
** Should be careful how I phrase that or the US might invade me.