Either you won't get enough voltage, and the car will stop once your battery is discharged, or you'll get excessive voltage, and you could end up actually overloading the battery and causing it to rupture, starting a fire, etc.
Bad voltage regulator
A bad voltage regulator can cause an overcharging condition. Check the wires going to the regulator for corrosion and make sure the regulator has a good ground.
The voltage regulator for the alternator is in the computer. If the voltage regulator in the computer does not work, you can add an external voltage regulator and then your battery will charge normally. Make sure to check the ground on the computer. If the ground is bad on the computer, then the computer will not regulate the voltage to the alternator properly.
It is built into your alternator
Yes it can.
Voltage Regulator bad
It is probably a bad voltage regulator. Sometimes they are located in the alternator and can go bad in a new one. On Ford vehicle the voltage regulator is separate from the alternator.
No
The voltage regulator is built into the alternator. I found this out when I was given an alt with a bad VR and was pushing 19v instead of 12.
Bad adjustment
In all probablility the voltage regulator is bad.
Bad voltage regulator