Standard Operating Procedure for Determining the Undercharged State of Electric Forklift Batteries in Winter

This procedure is applicable to two types of batteries: lead-acid batteries and lithium batteries. It clarifies the determination indicators, operation methods, responsible entities and abnormal handling procedures for undercharged states in winter, so as to ensure rapid identification of undercharging risks and eliminate the use of batteries in a deep undercharged state.

1. Core Criteria for Determining Undercharged State

The core definition of battery undercharging in winter is "depth of discharge > 70%" (remaining capacity < 30%). Combined with the battery characteristics in low-temperature environments, quantitative determination criteria are formulated by battery type:

2. Scenario-specific Determination Methods (Operation Steps + Responsible Entity + Execution Frequency)

(1) Pre-operation Predictive Determination (Responsible Entity: Forklift Operator; Execution Frequency: Once per pre-shift inspection daily)

Operation Steps for Lead-acid Batteries

1. 1.Turn off all electrical equipment of the forklift and let the battery stand for 10 minutes before measuring the no-load voltage.
2. 2.Use a suction-type hydrometer to test the electrolyte density, with at least 2 measurement points per cell.
3. 3.If the voltage < 12.4V or the density < 1.25g/cm³, the battery is determined to be undercharged, and the forklift is prohibited from operation.

Operation Steps for Lithium Batteries

1. 1.Start the forklift and check the remaining capacity displayed on the BMS screen.
2. 2.Access the system background to view the single cell voltage (equipment authorization required).
3. 3.If the displayed capacity < 30% or the single cell voltage is lower than the corresponding threshold, the battery is determined to be undercharged and must be charged immediately.

(2) Real-time Determination During Operation (Responsible Entity: Forklift Operator; Execution Frequency: Once every 30 minutes / after each batch of tasks)

Universal Voltage Monitoring Method

• Lead-acid batteries: Let the forklift idle briefly during operation and measure the working voltage. If the voltage drops by > 1.5V compared with the no-load voltage, it is determined as a precursor to undercharging.
• Lithium batteries: Observe the SOC change on the BMS. If the SOC drops by > 10% within 10 minutes (without overloading or sudden acceleration), it is determined as abnormal undercharging.

Power Attenuation Determination Method

1. 1.During no-load driving, press the accelerator pedal to 50% stroke. If the forklift accelerates slowly or the motor makes abnormal noise, the battery is determined to be undercharged.
2. 2.During climbing with a load (80% of the rated load capacity), if the climbing capacity decreases significantly (by > 30% compared with the normal state), the battery is determined to be undercharged.

Alarm Prompt Determination Method

• Lead-acid battery forklifts: If the power indicator light flashes or the buzzer alarms, the battery is directly determined to be undercharged.
• Lithium battery forklifts: If the BMS issues a "low battery alarm" or "voltage abnormality alarm", stop the forklift immediately for determination.

(3) In-depth Determination After Operation (Responsible Entity: Equipment Maintenance Technician; Execution Frequency: Once per post-shift inspection daily)

Supplementary Testing for Lead-acid Batteries

1. 1.Measure the voltage before charging. If the voltage < 12.0V, the battery is determined to be in a deep undercharged state.
2. 2.Observe the voltage rise rate during charging. If the voltage rises by < 0.5V within the first 2 hours, combined with the electrolyte density test result, the battery is determined to have sulfation-induced undercharging (a precursor to irreversible damage).

Supplementary Testing for Lithium Batteries

1. 1.Connect a professional detector to read the cell voltage and internal resistance data. If the internal resistance > 80mΩ, it is determined that the cell is damaged due to undercharging.
2. 2.Check the BMS fault records. If there are "over-discharge alarms" or "low-temperature discharge alarms", the battery is determined to have been used in violation of regulations in an undercharged state.

3. Notes on Determination Under Special Winter Working Conditions

Low-temperature Correction Principle

When the ambient temperature < 5℃, the no-load voltage determination threshold for lead-acid batteries is lowered by 0.2V (i.e., < 12.2V is determined as undercharged), and the single cell voltage threshold for lithium batteries is lowered by 0.1V to avoid misjudgment caused by low temperatures.

Misjudgment Prevention Scenarios

1. 1.For batteries that have just finished charging, let them stand for 2 hours before measuring the voltage to prevent interference from floating charge voltage.
2. 2.Loose battery terminals or line leakage may cause voltage abnormalities. Before determination, fasten the terminals and test the insulation performance first.

4. Handling Procedure for Undercharged State

1. 1.Once the battery is determined to be undercharged, stop the operation immediately, drive the forklift slowly to the charging area, and prohibit sudden acceleration or climbing.
2. 2.Undercharged lead-acid batteries: Recharge according to the winter charging standards (ambient temperature 10℃-25℃ + staged charging + 1 hour of floating charge). Deeply undercharged batteries need to undergo equalization charging.
3. 3.Undercharged lithium batteries: Activate the low-temperature charging protection mode, prohibit charging below 0℃, and put the battery into use only after the SOC reaches above 80%.
4. 4.For batteries determined to be undercharged for 3 consecutive times, the equipment maintenance technician shall conduct a comprehensive inspection to identify irreversible damage such as sulfation and lithium plating.