How to measure remaining capacity in my LiFePO4 battery?

Measuring Voltage

To get an initial estimate of your LiFePO4 battery’s state of charge, use a multimeter to check the voltage. A fully charged LiFePO4 battery typically reads around 3.6-3.7 volts per cell. As the battery discharges, the voltage will decrease. By checking the voltage, you can determine if the battery is above 50% charged, in the middle, or below 50% charged. However, this method is not as accurate as a capacity test, as the voltage can drop due to various reasons such as internal resistance or a faulty battery management system.

Using a Capacity Test Tool

To get a more accurate measurement of your LiFePO4 battery’s remaining capacity, use a capacity test tool such as a battery tester or a load tester. These tools apply a controlled load to the battery and measure the amount of time it takes to discharge to a specific voltage level. For example, a capacity test tool might load the battery to 2.8 volts per cell and measure the time it takes to reach that voltage. The resulting capacity reading will give you a more accurate measurement of the battery’s remaining capacity.

Understanding Capacity Readings

When interpreting capacity readings from a capacity test tool, keep in mind that the reading is typically expressed in ampere-hours (Ah). For example, if your battery has a capacity rating of 100Ah and the capacity test tool reads 80Ah, the battery has lost 20% of its capacity. This reading can be used to estimate the battery’s remaining life, although other factors such as age and maintenance can also affect the battery’s performance.