How to Identify When To Stop Using A Lithium Cell?

Measuring Capacity and Internal Resistance

Measuring a lithium cell’s capacity and internal resistance is crucial in determining its remaining lifespan. Use a battery tester or a device with a built-in load to measure the cell’s capacity and internal resistance. A good rule of thumb is to stop using the cell when its capacity falls below 80% of its original value. For example, if the cell has a rated capacity of 10Ah, replace it when its capacity drops to 8Ah or lower. To measure internal resistance, use a device that can apply a load to the cell and measure the resulting voltage drop. A higher internal resistance indicates a cell in decline.

Monitoring Voltage and Temperature

Monitoring the cell’s voltage and temperature is essential in identifying signs of degradation. A healthy lithium cell will maintain its voltage during discharge, and its temperature will remain within a safe range (usually between 10°C and 30°C or 50°F and 86°F). If the cell’s voltage rises during discharge or its temperature exceeds the safe range, it may be a sign of internal degradation. For example, a 12V lithium cell should maintain its voltage above 10.5V during discharge. If the voltage drops below 10V, it may be a sign of internal degradation. Use a multimeter or a device with a built-in voltage monitor to track the cell’s voltage and temperature.

Understanding State of Charge and State of Health

Understanding a lithium cell’s state of charge (SOC) and state of health (SOH) is critical in determining its remaining lifespan. SOC measures the cell’s current capacity relative to its rated capacity, while SOH measures its overall health and reliability. Use a battery management system (BMS) or a device with a built-in SOC and SOH monitor to track the cell’s remaining capacity and health. A good rule of thumb is to stop using the cell when its SOH falls below 70%.