Anker® Astro 2nd Gen. 6400mAh (2A Output) External Battery Portable Battery Power Bank Charger with PowerIQ ™ technology for smartphones and tablets - SmartPort for maximum charging speed (black) (accessory)
the external battery, the device loads very quickly and it can load two times before it needs recharging itself. Unfortunately, the spare battery is a little hard, but I think that no other way, therefore, still full star number.