A power bank is necessary an outside battery in a sealed situation or case.It is so simple to connect power bank to your devices such as mobiles,laptops,as well as your tablets.Power bank used together a USB wire or cable; you can link it to a power source like as a laptop as well as mobile to charge the power-bank. User merely require connect the device to portable power bank after that it will starting or functioning by itself to recharge the phone battery.