Voltage characteristics of lead-acid batteries for forklifts

Time：2025-07-14 10:23:18

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To better use and maintain the lead-acid batteries of forklifts, a comprehensive understanding of their voltage characteristics is indispensable.

In fields such as logistics and warehousing, forklifts play a crucial role, and the lead-acid battery of forklifts, as their power source, has a decisive impact on the performance and working efficiency of forklifts. To better use and maintain the lead-acid batteries of forklifts, a comprehensive understanding of their voltage characteristics is indispensable.
1. Basic Principles of Lead-Acid Batteries
Lead-acid batteries are mainly composed of positive and negative plates, electrolyte, separators and other components. The active material on the positive plate is lead dioxide (PbO₂), while on the negative plate it is spongy lead (Pb). The electrolyte is generally a sulfuric acid (H₂SO₄) solution. During the charging and discharging process, a series of complex electrochemical reactions occur on the positive and negative plates, accompanied by the transfer of electrons, thereby achieving the mutual conversion between chemical energy and electrical energy.
2. Voltage Indicators of Lead-acid Batteries for Forklifts
(1) Rated voltage
Under normal circumstances, the rated voltage of a single lead-acid battery cell is 2V. However, in actual forklift applications, to meet the power requirements of forklifts, multiple individual units are connected in series to form battery packs with different rated voltages, such as 24V, 36V, 48V, etc. For instance, a battery pack composed of 12 individual cells connected in series has a rated voltage of 24V.
(2) Open-circuit voltage
Open-circuit voltage refers to the potential difference between the positive and negative terminals of a battery in an open-circuit state (when there is no current output). For fully charged lead-acid batteries, the open-circuit voltage is generally slightly higher than the rated voltage, approaching 2.1V per cell. When the battery is in different charging states, the open-circuit voltage will also change. The more fully charged, the higher the open-circuit voltage. As the discharge proceeds, the open-circuit voltage gradually decreases.
(3) Working voltage
The working voltage refers to the terminal voltage at which current flows through an external load during the battery's discharge process. When a forklift is in operation, the working voltage of the lead-acid battery varies with the discharge time and the size of the load. At the initial stage of discharge, the working voltage drops relatively slowly. As the discharge continues, especially when the battery power is consumed to a certain extent, the working voltage will drop rapidly. When the working voltage drops to a certain extent, it means that the battery power is about to run out and it needs to be charged in time.
(4) Charging voltage
When charging the lead-acid battery of a forklift, the voltage output by the charger is the charging voltage. To ensure the battery is fully charged, the charging voltage is generally higher than the open-circuit voltage of the battery. The common charging methods adopt three-stage charging, namely constant current charging, constant voltage charging and trickle charging. During the constant current charging stage, the charging voltage will gradually increase. After entering the constant voltage charging stage, the voltage remains constant. In the final trickle charging stage, the voltage will slightly drop to ensure that the battery is fully charged without overcharging.
3. Factors Affecting the Voltage of Lead-Acid Batteries in Forklifts
(1) Charging state
This is the most direct factor affecting battery voltage. A fully charged battery has a relatively high voltage. As the battery discharges, the chemical substances inside it constantly react, the concentration of sulfuric acid decreases, and the voltage gradually drops.
(2) Temperature
The voltage of lead-acid batteries has a negative temperature coefficient. For every 1℃ increase in temperature, the voltage of a single cell will drop by 4mV. In a low-temperature environment, the viscosity of the electrolyte increases, the ion diffusion rate slows down, the internal resistance of the battery increases, and the voltage drops. In high-temperature environments, the chemical reactions inside the battery accelerate. If heat dissipation is poor, overcharging may occur, which also affects voltage stability.
(3) Discharge current
The magnitude of the discharge current also has a significant impact on the voltage. When discharging with a large current, the polarization phenomenon inside the battery intensifies, and the voltage drop across the internal resistance increases, causing the terminal voltage of the battery to drop rapidly. For instance, when a forklift is moving heavy objects or traveling at high speed, the discharge current is relatively large, and the battery voltage drops at a faster rate than during normal operation.
4. Frequently Asked Questions and Answers Regarding the Voltage of Lead-Acid Batteries for Forklifts
(1) What should be done if the voltage of the lead-acid battery of a forklift is lower than the normal range?
If the voltage of the lead-acid battery of the forklift is found to be lower than the normal range, the first step is to check whether the charging equipment is working properly and whether the charging time is sufficient. If the charging equipment and time are both fine, it might be that the battery has malfunctioned, such as sulfation of the plates or drying up of the electrolyte. Plate vulcanization can be attempted to be repaired by methods such as de-vulcanization charging. If the electrolyte dries up, an appropriate amount of distilled water or special electrolyte needs to be added. However, if the battery has been in use for a long time and experiences abnormal voltage multiple times, it may be necessary to consider replacing it with a new one.
(2) How to determine the remaining power of a forklift's lead-acid battery through voltage?
Although there is a certain correlation between battery voltage and remaining power, it is not a linear relationship. Generally speaking, the remaining power can be roughly estimated by measuring the open-circuit voltage of the battery and combining it with the battery's discharge characteristic curve. However, this estimation method is affected by factors such as battery aging and temperature, and there is a certain degree of error.
(3) What causes the voltage of lead-acid batteries in forklifts to abnormally rise during the charging process?
During the charging process, if the battery voltage abnormally rises, it may be caused by the following reasons. One is that the charger malfunctions, with the output voltage being too high. It is necessary to check whether the output voltage of the charger meets the charging requirements of the battery. The second possibility is that there is a problem inside the battery, such as a short circuit in some individual cells, causing the charging voltage borne by other individual cells to be too high. At this point, the battery needs to be disassembled for inspection, and the short-circuited individual cells should be identified and repaired or replaced. The third reason is that the charging environment temperature is too high, which leads to a decrease in the internal resistance of the battery and an increase in the charging current, thereby causing the voltage to rise. The charging environment should be improved to ensure that the charging temperature is within an appropriate range.
Understanding the voltage characteristics of lead-acid batteries in forklifts can help us use and maintain forklifts better, promptly identify problems with the batteries and take corresponding measures, thereby extending the battery's service life, improving the working efficiency of forklifts and reducing operating costs.

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