In order to increase the voltage of the lithium battery to the original level, you can try the following maintenance steps:
1. Charging: Connect the lithium battery to the appropriate charger and charge it to the rated capacity of the battery.
This should consume the remaining electricity in the pool and restore it to good operating condition.
2. Constant discharge: Connect the battery to the load to discharge moderately. This will help balance the charge between the cell units and eliminate excess electricity.
3. Calibration: Electronic devices may gradually \"forget\" the actual level of lithium battery power.
Calibrating the lithium battery (if the device allows it) can help re-determine the supply voltage to more accurately show the remaining value of the charge. Please note that lithium batteries should be operated within the appropriate operating temperature range. If the temperature is too high or too low, it may cause permanent damage to the battery.