There are alternators rated at 16-18 volts, but they are used for late model diert track cars. They use the higher voltage to get a hotter spark for higher horsepower. They also have to run either a 16 volt or a special 16-12 volt dual post battery to run that alternator.
I agree with red58, unless you have a high load requirement (welder/winch/over-powered stereo) you don't need more than 80 amps.
