Power bank is very useful for our phone. in these as we know dat we use multimedia phone. nd everyone use multi application, like: whtsap.we chat. fb. gmail. but bcz of dat. battery of our phone discharge soon. in dat case we need power bank in emergency case. like we r out of home. or we r not near by any charger plug. and d one thing dat should b in power bank is much more mph. bcz of dat we can chatge many of tym.