This is the proper way to turn some portable charger like yours. This charger prevents accidental turn on by itself while you keep it in package. If you do not like this way, buy another type charger without this safety feature.

> The charger itself is charged and to keep it charging I have to press the on button

Man, are you sure you are sober?

If the charger is charged, you can't charge it any further.

If I were the charger, I'd told you something; be happy that chargers can't (yet) talk.