Hello friends I am going to give my own experience tips on buying power bank for mobile.
Frist check mobile battery capacity( mh) and power bank capacity( mh) , always take only high capacity power bank than mobile battery capacity.
When you go to buy power bank then see IS logo on the product.
Dont buy any type of power bank form roadside, because they give high capacity power bank but actually this are low capacity like 1200mh to 2000mh.
4.dont use power bank if they are overheating.