Ok, so I have a variable DC voltage source that changes as due to outside factors. The voltage ranges between 9 and 18 volts with a current between 1 and 3 amps. I want the voltage source to charge a 12 volt battery continuously until it is full. Whent he battery is full, the circuit should shut off delivering the voltage from the voltage source to ground. The input to the battery can be below 12 volts, however, I don't want the voltage to ever reach a value larger than that. Can someone please help me?