battery lifespan

i purchased a dell inspiron15r (5521) in month of June 2013.. and just after the warranty has expired, the battery of this product has experienced permanent failure..

now my question is

what is the average battery life span of a dell laptop battery ? only 1 year and 4 months?

(PS: i am a moderate laptop user, not hardcore gamer or something.. i have seen battery of other brands lasting minimum to 3 years)..