If it uses the same 2032 battery that my craftsman uses then a 45k ohm resistor inline with the power source will step down your voltage so that the remote only drops 3v. I looked up the specs for the battery and it's a .2mA battery, with 3v that comes to 15k ohms of resistance ( at the least) on the circuit board of the remote. Now apply 12v and the same current and you get a total of 60k ohms, we already know the remote is 15k ohms, so you need 45k ohms more. This will put the remote still getting .2mA at the most and the 45k ohm resistor drops 9v so 3v is all that's left for the remote.