Powerbank is very usefull thing.i have also one, when ever you go for any journy and suddenly you see your mobile phone has out of battery then it will help you. in every place you cant find any place to charge your mobile but with the help of powerbank you can charge it anywhere in any place.it is not to much costly . and also not a big thing to carry . you can carry it in any pocket of your bag. I suggest everyone must buy a pawerbank. now everyone uses smart mobile phone, so they need their mobile alowyes chagre up