Does the battery just sit there after you start the car?

Your battery sacrifices some voltage during the car starting process. If you were to measure the voltage remaining in your battery just after you started your engine, you would find a voltage remaining somewhere between 11.7 volts and 11.3 volts on a good battery. If your battery is not so good, then the voltage remaining will be less.
While your car is running, the alternator acts as a recharging agent. The alternator sends voltage back into the battery until it reaches its top voltage storing capacity. In most modern vehicles, the alternator senses when the....