Why is there a fan in the DCB118 charger?

This charger is equipped with an in internal fan to cool the battery while charging.  The fan pulls air in around the battery to cool it and then blows this air out through the charger vents. Cooling the battery in this manner allows a hot battery to cool down faster so that it will charge faster. The fan also cools the battery while charging so that the battery is ready for use straight out of the charger.