[HawgRyder]

Everything about batteries is figured in Watts....or Volts X Amps.
When you start a car...you use a certain amount of Watts (amps @ battery voltage).
If we say that is takes 1200 Watts to start....you will need to put that back into the battery to bring it back up to where it was before you started the car.
So.....1200 Watts = 12 Volts at 100 Amps.
If your alt kicks out say 55 Amps per hour, it will take almost 2 hours to recharge the battery (that's 2 hours of driving above idle speeds).
When you run the numbers, you will see that in most cases, the alt will not return the battery to full in normal day to day driving (unless you have a long commute).
These are all approximate numbers....but you will get the idea.
A battery tender or trickle charger is the answer....to have the battery up to snuff every morning...and give you a good sense of comfort about the car during the day.
BTW....in cold climates (like up here in Canada) on really cold morning....we might use 5 times the normal Amps to start the car!!
Good luck
Bob