This data shows an additional point that needs to be considered particularly for devices that have embedded batteries. For these devices, when the battery wears out, the device can no longer be used since the battery is not replaceable. All rechargeable batteries have a finite number of times that they can be charged and discharged. This data shows how the battery performance degrades, cycle by cycle, as a result of charging to slightly different peak voltages. Users can see that in the early cycles charging to a slightly higher voltage will yield higher single-cycle capacity, but only for a little while. A cell that is charged even 50 or 100mV higher than the recommended 4.2V maximum will wear out much faster as a result of being slightly overcharged on each cycle. Some devices with embedded cells will intentionally “undercharge” their batteries in order to maximize their service life.