Constant current mode to measure total energy capacity of battery

Using Constant Current (CC) mode is the standard, most accurate, and most commonly used method to measure the total energy capacity of a battery (in Ah or Wh). This method involves discharging a fully charged battery at a fixed current rate while monitoring voltage until a designated cut-off voltage is reached

• Start Discharging: Apply the constant current load.
• Monitor Voltage: Log the voltage at regular intervals (e.g., every 60 seconds).
• Terminate on Cut-off: Stop the timer as soon as the battery voltage drops to the pre-set cut-off voltage.

B. Total Energy in Watt-Hours (Wh) - More Accurate

For better accuracy (since voltage drops during discharge), calculate the energy at each step and integrate over time.

Practically, this is done by calculating the average voltage during small intervals:

4. Key Factors Affecting Results

• Discharge Rate: Lower currents generally yield slightly higher capacity; higher currents (faster discharge) reduce usable capacity.
• Temperature: Elevated temperatures can increase capacity but shorten battery life.
• Voltage Drop: As the battery discharges, internal resistance causes the voltage to drop; the test ends when it reaches the minimum safe threshold.

Metric	Formula	Best For
Capacity (Ah)		Quick estimation, standard testing
Energy (Wh)		Accurate measurement, Li-ion batteries

In Constant Current (CC) mode, you determine a battery's energy capacity by discharging it at a fixed current until it reaches a safe cut-off voltage. While CC mode directly measures charge capacity (mAh), calculating total energy (Wh) requires tracking the falling voltage throughout the test.

• Accuracy: Unlike using a simple resistor (where current drops as voltage drops), CC mode keeps the "stress" on the battery consistent, providing a standardized discharge curve.discharge curve.
• Comparability: It allows you to calculate Peukert’s Law effects, seeing how the total available energy changes at different discharge rates (e.g., 0.5C vs 2C).

What is the chemistry and nominal voltage of the battery you are testing? Knowing this helps determine the optimal discharge rate (C-rating) and cut-off voltage for your specific test

• Electronic Loads: Professional devices like the Neware Battery Tester or Rohde & Schwarz DC Power Supplies automate CC discharge and log Wh data.
• DIY Solutions: You can build a circuit using a MOSFET, an op-amp, and an Arduino to maintain current and cut off at the right voltage.