Self-discharge is the slow loss of charge a lithium cell experiences even with no load connected. Measuring it correctly helps you judge cell quality and set a sensible storage interval.

How Is Self-Discharge Measured and What Rate Is Normal?

Two Common Test Methods

The open-circuit voltage method charges the cell fully, lets it rest, then stores it at a controlled temperature while its terminal voltage is checked periodically. A gradually falling voltage reflects self-discharge, so it is fast and widely used for incoming inspection. The capacity method fully charges the cell, stores it, then discharges it at a known current to the cut-off voltage and compares the delivered capacity with the expected value. It is slower but more accurate.

What Rate Is Normal

For a healthy lithium-ion or polymer cell, a self-discharge of roughly 2% to 5% per month at room temperature is common, though the exact figure depends on chemistry and state of charge. High temperature, a high state of charge and aging all speed it up. Cells showing abnormal leakage should be isolated.

For long storage, keep cells near 40% to 60% state of charge in a cool, dry place and top up periodically. Test conditions and acceptance limits are agreed per project.