Create 9V Battery Charger using an Adapter?

Hi , i've created a robot that works on a 9V Battery , i hope to make the robot charge on its own not having to take out the battery and recharge it or replace the battery , can i do this with a 1 Amp Adapter set at 12v?

Also how do i know if the battery is half filled , empty or full?
can i create something like green led for full , blue for half , red for empty?

thanks

What battery chemistry?

i don't know its just written on it 0% Cadmium 0% Nickel!