Why does my moped battery charger say battery is full the second I plug it in?

I have a 24 volt 1.5 amp battery charger that charges two 12 volt 12 amp batteries. I tested the voltage coming out of the two batteries combined and I get 18 volts. So it is obvious it needs a charging.

I tested the voltage coming out of the charger when the light is green (done charging) and it is 27 volts, which is enough to charge two 12 volt batteries.

So my question is, is the charger still charging when the light is green other than red??

thanks