First, visual inspection can be performed to check for abnormalities such as bulging, leakage, and burning. When battery faults cannot be determined visually, open-circuit voltage testing and on-machine capacity testing of the lithium-ion battery pack are required. Batteries requiring on-machine testing for open-circuit voltage and capacity testing are categorized as batteries with abnormal voltage, over-discharged batteries, batteries with abnormal discharge time, and batteries that overheat during charging.
I. Using a multimeter to test the condition of an electric vehicle battery
The most accurate way to test battery capacity is to fully charge it and then test it with a discharge tester. C=W=IUt, that is, the capacity is equal to the discharge current (amperes) x the voltage (volts) x the time (seconds or hours). Generally, the rated capacity is discharged at a rate of 0.5 to 2 times. For example, a 12AH battery is considered qualified if it is discharged for two hours at the rated voltage and current after being fully charged. The current is inversely proportional to the discharge time and discharge capacity. The larger the discharge current, such as 2 times the rated capacity, the longer the discharge time will be and the discharge capacity will be around 8AH. Conversely, using a rate of 0.5 times the rated capacity can discharge for more than two hours and can discharge 15AH.
II. Professional Testing Methods for Lithium-ion Battery Packs in Electric Vehicles
1. After fully charging the battery, connect the battery, ammeter, and resistance wire.
2. Internal open circuit in the battery. Some electric vehicles have an internal open circuit in their lithium-ion battery pack, which manifests as voltage in the battery but no current; the vehicle has power but the motor does not turn. If replacing the battery pack resolves the issue and the vehicle functions normally, then the problem lies with the battery.
3. If the green light on the charger does not change during charging but remains on when the battery is unloaded, it is generally due to a lack of water or dilute sulfuric acid inside the battery. After opening the battery cover, unscrew the one-way valve or safety valve and inject an appropriate amount of special replenishing fluid into the battery. Charge for 6-10 hours until the battery switches to the desired state.
4. If the electric vehicle has a short driving range, check whether the no-load current and running current of the whole vehicle are too high. The no-load current should not exceed 1.2 amps, and the running current should not exceed 7.5 amps when the vehicle is driven with a load of 75kg, a speed of 20km/h, and on a flat cement or asphalt road. If the above situations occur, replace the controller or motor and test again.
