Yes, it is better to have Power bank for changing different devices or gadgets at a time rather than just smartphone. Amazon.com is offering various branded power bank as discounted sale which help us to choose and buy Multi purpose Power bank with different features. Few of them from Amazon are as follows;
Multipin Portable Power Bank 4400mAH with LED Indicator for Mobile Phones, Tablets, Mp3, Mp4 Players and its price is Rs 1900 at the moment. Ref: http://www.amazon.in/Multipin-Portable-4400mAH-Indicator-Tablets/dp/8429392157?tag=googinhydr18418-21
Cool Yellow - ZOON 2800 mAh - Portable USB Charger - Power Bank - Emergency LED Flashlight (SAMSUNG Genuine Batteries) for Rs 699 at the moment.