Bats can live up to twenty-thirty or more years.
More Info: Unlike similar mammals of comparable size, bats enjoy a lifecycle more than 3.5 times greater once they escape the perils of youth. Five species are currently on record as surviving more than 30 years in the wild. 
The Perils of a Bat Pup
Baby bats are called pups and are usually born one at a time once a year. The baby bat clings to its mother, drinking her milk until it is old enough to fly on its own and capture its own food. Depending on the species, bats can generally leave their mothers and fly in about three weeks. Before this time, bat pups experience high mortality rates, as they are susceptible to many dangers before they can fly.
A mother bat is attached to her baby and provides food and protection for her pup until it is ready to exist independent of her. Yet, if a baby bat falls from its mother, she will not come to its rescue. Sadly, it will either die from the fall or will be eaten by predators. Bat pups are also more susceptible to disease and parasites. 
Theorized Factors Affecting Lifespan
Because it tends to live longer than other mammals of similar size, the bat’s lifespan is a matter of research interest. Researchers are attempting to isolate the factors of a bat’s lifestyle that add to its longevity. Analysis conducted by researchers from the Department of Biology, University of Maryland have revealed that the “bat life span significantly increases with hibernation, body mass and occasional cave use, but decreases with reproductive rate.” The bat’s diet and colony size appeared to have no affect on longevity.
 Wilkinson, Gerald S. , and Jason M. South. “Life History, Ecology, and Longevity in Bats.” Aging Cell 1.1 (2002): 124-131. Print.
 “Encyclopedia Smithsonian: Bat Facts.” Smithsonian. N.p., n.d. Web. 18 Oct. 2011. http://www.si.edu/Encyclopedia_SI/nmnh/batfacts.htm