The life of a lithium ion battery is measured by number of cycles. Each cycle corresponds to a full capacity discharge from 100% to 0%. On average, a cellphone’s battery has a capacity of 400 cycles. Research has shown that the total number of cycles available for a battery is directly related to how long you keep it charged at 100%. For example, your can triple the number of cycles of a lithium ion battery by charging to a capacity of 80% instead of the maximum 100%.
You get 400 cycles if you hold your battery charge level at 100%
You get 1200 cycles if you hold your battery charge level at 80%
You get 3000 cycles if you hold your battery charge level at 60%