My battery is putting out too much voltage..do I need a new aternator?

Possibly. Are they willing to guarantee their 'diagnosis'?Depending on the cost of the alternator VS. the cost of diagnosis is it worth the gamble?

if it is overcharging then the reglator inside the alt is probably shot you will need a new alt

battery when votemeter checked shoul be 12-12 1/2 volts , shoul reed 13 if alternator is working when engine is running