You can expect your battery to last about 3-6 years. (Then again, many owners claim their batteries are still going after 7 years.) Then again, you have between 700 and 800 charges, so if you charge the battery, let us say, every day, it will indeed last less than the average battery life span.
Lithium batteries usually don’t just stop working altogether, what happens is they gradually lose their capacity over time.
To prolong the life of your battery it’s suggested that you avoid discharging it completely, and the big thing is to make sure that you charge it at least once every couple of months.