Used to run a wireless communication store over the summers during school...
you are lucky if you get a year to year and a half out of a battery.. they have about 300-350 charges in them...so depending on how often you need to charge your phone.. it could last you a lot longer...
try not to charge your phone unless you have to.. if you are charging it every night..even when not needed..its taking from the life of the battery.. for most people..if you get a year out of the battery...you did well.