I now have a fairly long experience of this battery Anker, and longevity surprised, for a weight and size that are very reasonable. A recommended point, however: buying a powerful charger (30 watts), because with the small charger "type" smartphone, LONG is, recharge 15,000 mA at 5 volts (include more than half a day).
The battery Anker, she once busy, holds a fantastic time .....
I HIGHLY recommend .... And not just for IPhone, of course!