The primary battery can only be discharged once, and the secondary battery can be repeatedly charged and discharged. The rechargeable battery undergoes reversible changes in the volume and structure of the electrode during discharge. Therefore, these changes must be adjusted during the design. The interior of the primary battery is much simpler. Because it does not need to adjust these reversible changes, the mass specific capacity and volume specific capacity of the primary battery are both larger than the general rechargeable battery, but the internal resistance is much larger than that of the secondary battery, so the load capacity is lower. In addition, the self-discharge of the primary battery is far Smaller than secondary batteries.