Power Bank a device use to charge your mobile, i-pad, i-pod, etc. You can get it online or can get it from any store. But, my advice is to buy it online as it will save your money. Buy a better quality power bank. If your power bank is digital it will be easy for you to know that it’s charged completely.
But, if it’s not digital than you have to charge it for until, 3 hours until the red light turns blue. It’s really very helpful device if you go on a trip or picnic.