MiPow Power Cube 8000M - external mobile battery for smart phones, MP3 players, tablets and portable game systems with built-in micro USB port (8000mAh), orange (accessory)
I'm very satisfied with this device, I can with my Galaxy S4 with music, Ingress (consuming 3D game geocache like, attracts a lot of energy) at full screen brightness, GPS, WLAN, etc. almost all day by the run city. Even when multi-day hikes a must: