Generally, unique characteristics of material and structure have determined lithium-ion battery's lifetime. Battery lifetime calculated as per material and structure is called theoretical lifetime. Yet actual lifetime of lithium battery during work is often shorter than theoretical lifetime, which is caused by capacity's non-work loss.

This non-work loss is affected by following factors:
1. Side effects of lithium-ion battery;
2. Irreversible loss of active substances in lithium-ion battery;
3. To high-capacity li-ion battery, high work current and slow heat dissipation can easily damage battery structure;
4. Capacity should be provided by lithium battery for maintenance purpose if additional safety protection measures needs taking on lithium battery.

Capacity decreases of lithium battery is reflected in the course of lithium battery charge, discharge and self-discharge.
1. Charge time shortens as cycle times increase. Charge platform of lithium battery is 3.7V to 4.2V, when charge capacity accounts for over 90% of total charge capacity. As cycle times grow, voltage rise speeds up and charged capacity lessens.
2. Discharge platform of lithium battery falls into 4.1V-3.6V. In this phase, discharge capacity accounts for over 90% of total capacity. Increasing cycle times will cause lower discharge platform and discharge capacity.
3. As cycle times increase, proportion of self-discharge capacity in total capacity becomes larger. Nevertheless, discharge platform of lithium battery fast decreases.

The feature that short lifetime of lithium-ion battery is reflected by decreased capacity illustrates that: lithium battery lifetime is finite, just like development of any thing. Capacity decrease is a form of quantitative to qualitative changes. This form defines that ways of extending lithium battery lifetime should consider scientific charge and discharge, and reducing self-discharge.