Battery life will vary depending on your riding style and charging practice. Typically, Lithium Ion (Li-Ion) batteries last around 600 charges where the capacity has decreased to 70%.
This can be extended by following a few rules.

Never leave the battery in a flat condition, always recharge after the battery is flattened.
Store your battery in a cool place.
Charge your battery every 2 months if it is not being used.
Avoid running your battery flat. Aim for 70% discharge.
Ride a a speed that draws lower watts from the battery. (avoid long high power situations)

There are improvements in cell quality and charging happening all the time, so when it is time to renew your battery there are sure to be larger capacity and longer lasting packs available.