It's not how much you use it as much as it is how low you let it go before charging it. Best life is to charge at 50%. If you let it get down to 0% (or close to that) every time, it probably won't last more than a month or two. 300-500 charges is about normal if you let it go to 20%. But 50% might give you as much as 1,500 charge cycles. (And the battery discharges by itself. If you're going to leave the phone turned off for long periods, store it with about a 50% charge - it self-discharges slower like that.)