Some bats do hibernate.

In colder regions, some bats choose to hibernate in high humidity sheltered spots such as caves, houses, or barns while others will simply migrate to warmer regions. For example, of the eight bat species known to the state of New Hampshire, five hibernate for the winter.

How Do Bats Hibernate?

Like other mammals that hibernate, the bat enters a dormant state where its body's metabolism slows down significantly.  Its body temperature lowers considerably and its heart rate can decrease from 1,300 beats per minute needed for flight to as low as 20 beats per minute.  With a significant metabolism decrease the bat can then rely on its fat reserves to survive as its food source is not available in the colder months.

What Happens If Hibernating Bats Are Disturbed?

An interesting study found that bats that are disturbed during their hibernating period require 107.9 mg of fat for arousal from the homeothermic stage and even more if it flies.  This fat consumption would be needed each time the bat is aroused.  Because bats are generally known to arouse naturally to eliminate waste and adjust body temperature, too many unexpected arousals could adversely affect the survival of the bat depending on its size since there are generally no available food sources at the time of the bat's hibernation.