new iphone 7plus left charging overnight but he battery only decreases

Hi.

Powerbanks are not meant to charge phones. They are meant to supply power to sustain the operation of phones on the go.

When you connect a powerbank to your phone, your phone battery charge percentage may go up somewhat. But that does not mean it charges your phone satisfactorily.

Use a wall socket charger to charge your phone. Keep the charger connected until the charger gets cool to touch. This means your battery is full and your phone charge circuitry has stopped charging the battery. Now you have 100% charge on your battery. If the battery charge percentage is not 100%, then use another charger to test. You can use any decent USB battery charger if you do not have another iPhone / iPad charger.

Still below 100% charge ? Your phone cuts charge power earlier than the battery gets full or phone battery is defective. Call help from Apple Care Center.

Hope this helps.

Hi

Power bank may need charging next time you charge use the mains socket.

Iphone will charge up to about 85% then slow down to help the battery.

Go to i books download ios 11 user guide &iPhone 7 guide both are free.

Cheers

Brian 🇬-1F1E7;

What happens when you charge it in a normal socket with the cable that came with it?

Try that, and if there is still a problem take it back.