This illustration shows the importance of precision in the output regulation point for a Li-Ion battery. For example, a designer starts with a 950mAH nominal battery and charges / discharges it hundreds of times. Each time it is recharged, the terminal voltage is regulated to precisely 4.2 volts. Under these conditions, after 500 cycles, the cell can still deliver about 850mAH at the same load current as it did when it was new. This is a relatively mild degradation, and shows that a battery like this could provide good service for many months or years depending on how often it is used. However, if the charge circuit regulates just 100mV too high on each recharge, as in the 4.3V curve, after about 200 – 250 cycles the degradation curve becomes very steep and the cell quickly becomes unusable. So, a precision regulator circuit is required for the charger in order to maintain battery performance and extend the battery’s service life.