A "12 volt battery" puts out about 14 volts when no current is being drawn. It drops down under load to 12 volts or lower depending on the amount of load.
The voltage regulator keeps the battery at 100% voltage under no load conditions, so it stops charging at about 14.2 volts, and charges at anything less.
Careful with your wording, the battery doesn't put out 14 volts. It's the alternator that gets the voltage of the system that high. The battery doesn't go above 12.6 normally, as said previously (although I don't think I've ever had mine that high, it's usually at 12.2 or so with the car off).
If you have a load that's dipping your voltage under 12 regularly, you need a beefier alternator and perhaps an extra batteries. I'm into car audio and we run into questions about this all the time. Kids can't be running 4,000 watts off of their stock electrical systems!