1、 Preparation before testing: Clarify the basic information and safety precautions of the battery

1. Basic information confirmation

Type: Commonly used are lead-acid batteries (including ordinary rich liquid type, maintenance free sealed type) and lithium-ion batteries (commonly used in new energy vehicles), with slight differences in their testing methods (lead-acid batteries can measure electrolyte density, lithium batteries cannot).

Specification: Check the rated voltage (12V passenger car/24V commercial car), rated capacity (such as 55Ah, 70Ah, referring to the discharge capacity at a 20 hour rate), and cold starting current (CCA, such as 500A, low-temperature starting capability) marked on the battery casing.

Service life: Lead acid batteries typically have a lifespan of 3-5 years, while lithium batteries have a lifespan of 5-8 years. After exceeding the lifespan, the probability of capacity degradation increases significantly.

2. Safety precautions

Before inspection, ensure that the vehicle is turned off and all electrical devices (lights, air conditioning, sound system, etc.) are disconnected.

Wear insulated gloves during operation to avoid metal tools coming into contact with both positive and negative poles (to prevent short circuits and sparking).

When testing lead-acid batteries, stay away from open flames (to avoid hydrogen explosions). If the electrolyte leaks, it should be neutralized with baking soda solution and direct skin contact is prohibited.

2、 First level inspection: Appearance and basic voltage inspection (quick preliminary judgment)

1. Appearance inspection (visually eliminate physical faults)

By observing the battery casing, terminals, and electrolyte status, clear damage can be ruled out:

Shell: Whether it is swollen, cracked, or deformed (bulging is often caused by overcharging or high temperature leading to plate vulcanization, and the capacity has been severely reduced).

Terminal post: Whether it is oxidized or corroded (appearing as green or white powder, which can cause poor contact and affect power supply, and needs to be sanded and cleaned).

Electrolyte (only for rich electrolyte lead-acid batteries): Observe whether the liquid level is between the "MIN-MAX" scale and whether the color is clear (turbidity or blackening indicates electrode detachment and capacity failure).

Maintenance free battery observation window: Some maintenance free batteries have color indicators (different brands have different meanings, please refer to the manual). Common rules:

Green/Blue: Adequate capacity and good condition;

Yellow/Orange: Insufficient capacity, charging required;

Black/Colorless: Capacity depleted or battery failure, replacement is required.

2. Static voltage test (no load voltage, quickly evaluate remaining capacity)

Use a digital multimeter (accuracy ≥ 0.01V) to measure the voltage between the positive and negative terminals of the battery, reflecting the "open circuit voltage" of the battery:

Operation steps:

Turn off the vehicle, turn off all electrical equipment, and let it stand for more than 1 hour (to stabilize the battery voltage).

Set the multimeter to the "DC 20V" position, connect the red probe to the positive pole (+) and the black probe to the negative pole (-), and read the voltage value.

3、 Secondary testing: Load and starting voltage testing (simulating actual working conditions)

Static voltage only reflects the "no-load state", and it is necessary to simulate the high current discharge during startup through load testing to determine the "actual power supply capacity" of the battery (core detection item).

1. Start voltage test (the simplest load verification)

Principle: At the moment of vehicle start-up, the battery needs to output hundreds of amperes of high current. If the voltage drops too quickly, it indicates insufficient capacity or excessive internal resistance.

Operation steps:

Set the multimeter to the "DC 20V" position and connect the probe to the positive and negative poles.

Ask the assistant to start the vehicle and observe the minimum voltage value at the moment of starting (quick reading is required).

Result interpretation (12V lead-acid battery):

Instantaneous starting voltage ≥ 9.5V: good capacity, normal starting ability;

Instantaneous voltage during startup 8.5V-9.4V: The capacity has slightly decreased, but it can still be used, but attention should be paid to charging;

Instantaneous startup voltage<8.5V: The capacity is severely insufficient or the internal resistance is too high to meet the startup requirements, and replacement is required.

2. Specialized load tester testing (professional level testing, recommended)

Using a battery load tester (also known as a "discharge fork", split and intelligent type), apply a constant load of 50% of the rated capacity of the battery (such as a 55Ah battery loaded with 27.5A current) for 15 seconds, and measure the load voltage:

Operation steps (taking 12V lead-acid battery as an example):

After the battery is left to stand for 1 hour, connect the tester (red clip positive electrode, black clip negative electrode).

Set the load current (usually 1/2 of the rated capacity, i.e. 0.5C discharge rate) and start the load.

After 15 seconds, read the voltage value and observe whether the battery has abnormal heating or bubbling.

Interpretation of Results:

Load voltage ≥ 10.5V: sufficient capacity, good health status (SOH ≥ 80%);

Load voltage 10.0V-10.4V: Medium capacity, can continue to be used, but it is recommended to charge regularly;

Load voltage 9.5V-9.9V: Severe capacity degradation (SOH 50% -70%), replacement is required;

Load voltage<9.5V: Capacity failure (SOH<50%), must be replaced.

Advantages: More accurate than starting voltage testing, it can simultaneously evaluate "capacity" and "internal resistance" (excessive internal resistance indicates plate vulcanization and short circuit).

4、 Level 3 testing: Capacity discharge test (accurate measurement of actual capacity)

Suitable for scenarios where the true remaining capacity of the battery needs to be confirmed (such as repair shop inspections, used car evaluations), the actual capacity is calculated through "constant current discharge → recording time".

1. Method: 20 hour rate discharge test (standard method for lead-acid batteries)

Principle: Continuously discharge the battery at 1/20 of its rated capacity until the voltage drops to 10.5V (12V battery). The discharge time multiplied by the current equals the actual capacity.

Operation steps (taking 70Ah battery as an example):

First, fully charge the battery (charger voltage 13.8V-14.4V, charge until the current stabilizes below 0.1C).

Connect the constant current discharge device and set the discharge current to 3.5A (70Ah ÷ 20=3.5A).

Continuously discharge and record the total time (in hours) when the voltage drops to 10.5V.

Calculate actual capacity: 3.5A x discharge time (h)=actual capacity (Ah).

Interpretation of Results:

Actual capacity ≥ 80% of rated capacity: qualified and can continue to be used;

Actual capacity 60% -79%: Capacity decay, recommended for low load scenarios (such as backup power);

Actual capacity<60%: Failure, replacement required.

2. Intelligent Capacity Tester (Quick Alternative Method)

Using intelligent battery testers (such as Mite and Bosch brands), the internal resistance of the battery is measured using the "AC injection method", and the actual capacity is calculated using built-in algorithms. There is no need for long-term discharge, and the results can be obtained in 3-5 minutes, making it suitable for rapid on-site testing.

5、 Lithium ion battery testing (for new energy vehicles)

The structure of lithium batteries is different from lead-acid batteries, and the electrolyte density cannot be measured. Special equipment is required to detect the cell voltage, internal resistance, and balance:

Cell voltage detection: Use a multimeter or lithium battery detector to measure the voltage of each cell (nominal 3.2V/3.7V for individual lithium batteries). If the voltage difference between cells is greater than 0.1V, it indicates poor balance and capacity will be limited by short board cells.

Internal resistance detection: Use an internal resistance meter to measure the internal resistance of each battery cell. If the internal resistance suddenly increases (such as exceeding 50m Ω), it indicates that the battery cell is aging or damaged.

Capacity detection: Read the remaining capacity (SOC) and state of health (SOH) through the onboard BMS (battery management system) of new energy vehicles, or conduct charge discharge cycle tests using a dedicated lithium battery charging and discharging instrument to calculate the actual capacity.

6、 Common problems and avoiding misjudgments

The static voltage is normal but the startup is weak: it may be due to excessive internal resistance of the battery (plate vulcanization), and a load tester should be used to measure the load voltage (rather than just looking at the static voltage).

Misjudgment of maintenance free battery observation window: The color of the observation window is affected by temperature and light, and needs to be cross verified with voltage testing. It cannot be used as a separate judgment basis.

Insufficient capacity of new battery: It may be due to long-term storage causing self discharge. After fully charging, retest. If it is still insufficient, it is a quality issue.