Power bank is useful gadget to charge our battery of cell phone especially when traveling or outside home.
my personal experience about power banks says:
please do not look at Chinese version or cheap power bank . I purchased iKare 20800 mah powerbank from snapdeal.
it may have not that capacity of power as listed on product.
it could damage our cell phone battery life,
it takes more time to charge fully,
loose usb port and
I recommend to use quality and standard powerbank for your cell phone.
buy specially from amazone huawei honor, lenovo, intex pb, anbrone that are few good powerbank available online