[Styrak]

A smart charger will change voltage constantly to charge the battery properly. A empty battery will need less voltage at the beginning. While it's charging the voltage will constantly go up (to compensate for the battery's voltage).

And no, a charger will not "detect" what charge a battery currently has. It's just senses what voltage the pack is at and charges according to that. You can look at the current voltage to see approximately where it's at, if your charger displays current voltage.