My fob was 12vdc.
I was looking to use the smaller keychain fob which was 3vdc and was looking into dc/dc converters or linear regulators but.....cant help you anymore than that.
I had this medium sized 12vdc fob/opener laying around after I called the Overhead Co. because I couldn't program the viser buttons in my jeep with the rolling code tech in the new opener. For whatever reason they sent me this fob and it just happened to be 12v. (does this make sense? I had put in a new opener a year before I did this to the bike)
