2026-10-13
Content
Dilute sulfuric acid (H₂SO₄) mixed with distilled water. It is the electrolyte that carries ions between the lead dioxide plates and the sponge lead plates inside every Lead Acid Forklift cell.
Sulfuric acid burns from contact with the electrolyte, and hydrogen gas explosions caused by gassing during charging in a poorly ventilated area. Both are preventable with correct equipment and routines.
Neither wins in every case. Lithium-ion suits multi-shift, fast-turnaround duty. Lead-acid suits single or double shifts, tight capital budgets and trucks that rely on battery weight as counterbalance.
The electrolyte in a Lead Acid Forklift battery is sulfuric acid diluted with distilled or deionized water. A fully charged cell holds roughly 35% to 40% acid by weight, which corresponds to a specific gravity of about 1.277 to 1.299 at 25°C (77°F). As the battery discharges, acid is consumed and the density of the liquid falls. That is why a hydrometer reading tells you how much energy is left in the cell.
The chemistry is a reversible reaction. During discharge, sulfuric acid reacts with the positive plate (lead dioxide) and the negative plate (sponge lead). Both plates convert partly into lead sulfate, and water is released into the electrolyte. During charging, the reaction runs backward. Lead sulfate returns to active material and the acid concentration climbs again.
Water is lost from a Lead Acid Forklift cell through electrolysis during charging, while the sulfuric acid stays in the cell. Topping up with acid would push the density above its design value, accelerate grid corrosion and shorten service life. Tap water is also unsuitable, because dissolved minerals such as chlorides and iron contaminate the plates. Distilled or deionized water is the only correct refill liquid.
The table lists typical readings for a traction cell with a full-charge gravity near 1.280. Readings change with temperature, so apply the correction supplied with your hydrometer.
| State of charge | Specific gravity (25°C) | Open-circuit voltage per cell | Open-circuit voltage of a 48V pack |
|---|---|---|---|
| 100% | 1.280 | 2.12 V | 50.9 V |
| 75% | 1.250 | 2.08 V | 49.9 V |
| 50% | 1.220 | 2.04 V | 49.0 V |
| 25% | 1.190 | 2.00 V | 48.0 V |
| Discharged | 1.160 or below | 1.95 V or below | 46.8 V or below |
All three designs use the same sulfuric acid chemistry. The difference lies in how the electrolyte is held inside the cell.
Free liquid electrolyte surrounds the plates. Water must be added regularly and the cells vent gas during charging. This design dominates traction duty because it tolerates deep daily cycling and offers the longest service life per dollar spent.
The electrolyte is absorbed into glass-mat separators. The valve-regulated case never needs water and spills far less if the container is damaged. Charging voltage must be controlled tightly to avoid drying out the mat.
Silica thickens the acid into a gel. Gel cells handle shallow cycling and standby duty well, but they are more sensitive to charge rate and generally cost more than a flooded Lead Acid Forklift pack of equal capacity.
A traction battery is not one large cell. It is a series string of 2-volt cells, each with its own plates, separators and electrolyte, linked by lead-plated copper connectors inside a rigid steel tray. The number of cells sets the voltage. A 24V pack contains 12 cells, a 36V pack contains 18, a 48V pack contains 24 and an 80V pack contains 40.
Tubular positive plates hold lead dioxide inside woven gauntlets. This construction resists shedding during deep discharge and is the main reason a traction Lead Acid Forklift outlasts a starter-type battery in the same duty.
Pasted flat grids carry sponge lead with expanders that keep the active material porous. Correct expander chemistry preserves low-temperature performance and charge acceptance.
Microporous polyethylene sleeves keep the plates apart while letting acid ions pass. Their pore size and thickness set the internal resistance of the cell.
Impact-resistant polypropylene jars sit inside a steel tray that doubles as counterweight. Cell covers are heat-sealed to prevent electrolyte leakage along the seam.
Lead-plated copper straps and welded posts carry high current with low voltage drop. Loose or corroded connections generate heat and are a leading cause of premature cell failure.
Flame-arrestor vent caps release hydrogen while blocking sparks from entering the cell. Many designs include a float that signals the electrolyte level at a glance.
When safety trainers ask what are the two most common hazards with the lead-acid batteries in electric forklifts, the accepted answer is acid burns and hydrogen explosions. Every other incident type, from heavy-lifting injuries to electrical shorts, is less frequent in most workplaces. Understanding the cause of each hazard makes the preventive steps easy to remember.
The electrolyte in a Lead Acid Forklift battery is corrosive. Contact with skin causes chemical burns, and a splash into the eye can cause permanent damage within seconds. Clothing, concrete floors and metal tools are attacked as well.
Typical exposure moments include topping up cells, removing vent caps, lifting a pack with a tilted tray, working around a cracked jar and handling wet terminals with bare hands.
When a cell passes about 2.35 volts during charging, water in the electrolyte splits into hydrogen and oxygen. Hydrogen is colorless, odorless and reaches its lower explosive limit at just 4% concentration in air.
A single spark from a loose plug, a dropped tool, a static discharge or an open flame can ignite the gas. Poor ventilation and covered cell vents increase the risk sharply.
| Task | Eyes and face | Hands and body | Additional measures |
|---|---|---|---|
| Watering cells | Splash goggles | Acid-resistant gloves, apron | Use a filling system or a dedicated pitcher |
| Reading specific gravity | Splash goggles | Acid-resistant gloves | Rinse the hydrometer in clean water after each cell |
| Cleaning terminals | Face shield and goggles | Gloves, long sleeves | Neutralize residue with a baking soda solution |
| Moving the battery | Safety glasses | Gloves, safety boots | Use a rated lifting beam or a battery exchange system |
| Cleaning up a spill | Face shield and goggles | Acid-resistant suit, boots | Contain, neutralize, then collect for proper disposal |
Remove the person from the battery area and take off contaminated clothing immediately, cutting it away if it clings to the skin.
Rinse skin or eyes with plenty of clean running water for at least 15 minutes. Hold the eyelids open during eye irrigation.
Baking soda is for floors and equipment. Applying it to skin or eyes can cause additional heat and irritation.
Arrange medical care even if the pain fades. Bring the product safety data sheet so clinicians know the exact chemical involved.
Hydrogen release is greatest in the last phase of charging, and again during equalization. Charging areas should be designed so the gas can never accumulate. Because the gas is lighter than air, it rises and collects under ceilings and in dead-air corners unless exhaust fans or natural ventilation carry it away.
Connect the charger plug to the battery before switching on the power, and switch off before disconnecting. Keep all smoking materials, open flames and welding work out of the area. Keep cell vent caps in place and the tray cover open so gas escapes freely. Use insulated tools and avoid placing metal objects on top of the battery.
Install dedicated exhaust ventilation sized to the number of chargers, mark the zone with warning signs, provide an eyewash station within a ten-second walk, and equip the area with a suitable fire extinguisher. Many sites also add hydrogen detectors that trigger fans automatically when concentration rises.
Local codes, including the battery charging requirements in OSHA 29 CFR 1910.178(g), set the minimum conditions for charging and changing batteries. Always confirm the rules that apply at your location.
The question of which type of forklift battery is better, lithium-ion or lead-acid, has no universal answer. A Lead Acid Forklift battery costs less to buy and has a long record of reliable service. A lithium-ion pack charges faster, needs less attention and delivers more usable energy per cycle. The correct choice depends on how many hours the truck runs, whether there is time to charge and cool a battery, how much capital is available and what the truck was designed to carry as ballast.
| Parameter | Lead Acid Forklift Battery | Lithium-Ion Forklift Battery |
|---|---|---|
| Typical cycle life | 1,000 to 1,500 cycles | 2,000 to 4,000 cycles |
| Time to full charge | 8 to 10 hours | 1 to 2 hours |
| Cooling time after charge | About 8 hours | None required |
| Opportunity charging | Not recommended | Supported |
| Energy efficiency | 70% to 85% | 95% or higher |
| Usable depth of discharge | About 80% | 80% to 100% |
| Watering | Required for flooded cells | Not required |
| Hydrogen during charging | Yes, ventilation required | No |
| Acid leakage risk | Present | None |
| Weight | Heavy, acts as counterbalance | Lighter, ballast may need to be added |
| Voltage behavior under load | Sags as charge falls | Stays stable until nearly empty |
| Cold-room performance | Capacity drops noticeably | Stable with built-in heating options |
| Upfront cost | Lower | Higher |
| Recycling path | Established, very high recovery rate | Developing |
Both chemistries lose usable capacity as they age. A common end-of-life threshold is 80% of rated capacity. The curve below shows an illustrative pattern for a well-maintained Lead Acid Forklift battery and a lithium-ion pack under similar daily duty.
The familiar 8-8-8 routine explains why a single Lead Acid Forklift pack fits one shift per day. The truck works for about eight hours, the battery charges for eight hours, and the cells then rest for eight hours so temperature settles. Running three shifts with this chemistry needs a second or third battery and a swap area.
The truck runs one or two shifts and has a natural gap for charging. Capital budget matters more than labor savings. The truck depends on battery mass as counterweight. A charging room, spare batteries and a trained watering routine already exist.
Trucks run around the clock with no time to exchange packs. Maintenance labor is scarce. Clean-room, food or pharmaceutical zones restrict acid and hydrogen. Short breaks can be used for top-up charging.
Purchase price tells only part of the story. A fair comparison counts the battery, the charger, the energy bill, watering labor, ventilation equipment, spare packs for multi-shift use and the expected replacement date. For a single-shift operation, a Lead Acid Forklift battery usually has the lowest total cost, because its low purchase price outweighs the extra energy and labor. As daily operating hours rise, the lithium-ion advantage in efficiency and avoided battery swaps grows with it.
A well-maintained Lead Acid Forklift battery routinely reaches 1,500 cycles, while a neglected one may fail in less than half that. Most early failures trace back to a short list of habits: partial charging, charging with low electrolyte, overheating and leaving cells discharged. The schedule below turns good practice into a routine.
| Interval | Task | Why it matters |
|---|---|---|
| Every shift | Disconnect and reconnect plugs carefully, check cables and connector housings for damage | Damaged plugs overheat and create sparks near hydrogen |
| After every charge | Check electrolyte level and add distilled water if plates are exposed or the level is low | Exposed plates sulfate permanently; overfilling pushes acid out of the cell |
| Weekly | Wipe the cell tops, inspect vent caps, record specific gravity of pilot cells | Surface acid film creates leakage current and corrosion |
| Weekly or every 5 to 10 cycles | Run an equalizing charge | Brings every cell to the same state of charge and reduces stratification |
| Monthly | Measure specific gravity and voltage of every cell, clean and grease terminals | Identifies weak cells before they drag down the whole string |
| Quarterly | Check tray condition, torque on connectors, charger output and cable insulation | Loose joints raise resistance and heat; charger drift shortens battery life |
Recharge when remaining capacity reaches about 20%. Charge in a ventilated area with the vent caps in place. Add distilled water after charging, not before. Keep the electrolyte below 49°C (120°F). Record every watering and equalization so patterns are visible.
Repeated short top-up charges that leave the pack half full. Running the battery until the truck stops. Adding acid instead of water. Wearing rings or watches near open terminals. Storing a discharged Lead Acid Forklift battery for weeks without charging.
| Symptom | Likely cause | Recommended action |
|---|---|---|
| Short runtime after full charge | Sulfated plates, aging, or an insufficient charge | Run an equalizing charge, then test capacity under load |
| One cell with low gravity | Internal short or a damaged plate group | Isolate the cell and have it tested or replaced |
| Electrolyte level falls quickly | Overcharging or a faulty charger profile | Check charger settings and voltage cut-off |
| White crust on terminals | Acid vapor and moisture reaching the lead | Neutralize, clean, dry and apply protective grease |
| Battery gets hot during charge | High charge current, low electrolyte or aging cells | Stop charging, let it cool, then inspect level and charger |
| Voltage drops sharply when lifting | High-resistance connection or weak cells | Inspect connectors and measure individual cell voltages under load |
Three numbers define a correct fit: voltage, capacity and physical dimensions. Voltage must match the truck controller. Capacity, measured in ampere-hours at a five-hour or six-hour rate, must cover the working shift with a safety reserve. The tray must fit the battery compartment, and the weight must meet the minimum ballast figure printed on the truck nameplate.
Common traction voltages are 24V, 36V, 48V and 80V. Higher voltage supports larger trucks with heavier lifting loads.
Ampere-hours determine runtime. Multiply by voltage to find energy in kilowatt-hours, a better figure for comparing different pack designs.
Length, width and height must fit the compartment with room for cable routing. Minimum and maximum weight limits protect truck stability.
| Step | Calculation | Result |
|---|---|---|
| Average current draw during the shift | Measured with a data logger or estimated from duty cycle | 120 A |
| Hours of work per shift | One shift with breaks excluded | 7 h |
| Energy needed | 120 A × 7 h | 840 Ah |
| Allowing 80% depth of discharge | 840 Ah ÷ 0.8 | 1,050 Ah required |
| Nearest standard 48V Lead Acid Forklift size | Round up to a standard cell model | 1,085 Ah |
This example is illustrative. Real current draw varies with lift height, load weight, travel distance and ramp use. Our engineers can size a pack from your truck model and duty data.
We design and manufacture traction batteries at our own plant, from grid casting to final load testing. Each Lead Acid Forklift pack is assembled to the voltage, capacity and tray dimensions specified for your truck, so installation is a matter of lifting the battery in and connecting the plug.
Compact trays for pedestrian pallet movers and stackers working in tight aisles.
A balanced option for smaller counterbalance and narrow-aisle models with moderate lifting duty.
The most widely used voltage for three-wheel and four-wheel electric trucks in warehouses and plants.
High-capacity packs for large counterbalance trucks and long, demanding shifts.
| Voltage | Cells in series | Capacity range (5-hour rate) | Typical truck class |
|---|---|---|---|
| 24V | 12 | 200 to 775 Ah | Pallet trucks, stackers |
| 36V | 18 | 250 to 930 Ah | Compact counterbalance, narrow aisle |
| 48V | 24 | 300 to 1,085 Ah | Standard counterbalance, reach trucks |
| 80V | 40 | 400 to 1,240 Ah | Heavy counterbalance trucks |
Custom trays, connector positions and capacities outside this range are available on request.
High-density lead alloy spines and woven gauntlets give strong deep-cycle endurance and resist active material shedding.
Alloy composition is selected to limit water loss, so cells need less frequent watering and gas less in the final charging phase.
Welded and coated against acid. The tray carries the weight, protects the jars during lifting and provides the ballast the truck needs.
A single-point filling kit tops up all cells in minutes, cutting contact with acid and removing the risk of over-filling.
Lead alloy is cast into grids, then pasted or filled with active material under controlled density and thickness.
Plates cure under controlled humidity and temperature so the paste bonds firmly to the grid and forms a stable crystal structure.
Plate groups are stacked with separators, welded into cell elements and fitted into jars, then connected in series inside the tray.
Cells are filled with sulfuric acid of controlled density and charged under a programmed profile that converts the paste into active material.
Every finished battery is discharged to verify capacity, checked for case leakage and inspected for connector torque and insulation.
Each pack leaves with a nameplate showing voltage, capacity, weight and serial number, and is secured on a pallet with protective covers.
| Test | What it verifies |
|---|---|
| Rated capacity discharge | Delivers the stated ampere-hours down to the end-of-discharge voltage |
| Cell voltage balance | All cells within a narrow tolerance at the end of formation |
| Specific gravity check | Electrolyte density matches the design value in every cell |
| Insulation resistance | No leakage path between the cells and the steel tray |
| Leak inspection | No electrolyte seepage at covers, posts or jar seams |
| Dimension and weight check | Tray size, plug position and weight match the order drawing |
Dimensioned drawings and connection diagrams are supplied before production so the pack can be checked against your truck.
We help select chargers with the correct voltage, current and charging profile for the Lead Acid Forklift pack you order.
Watering, equalizing and cleaning instructions are provided in printed and digital form for your service team.
Sulfuric acid diluted with distilled water. The solution has a specific gravity of about 1.277 to 1.299 when the cell is full and falls as the battery discharges.
No. Water evaporates during charging, and the acid remains in the cell. Add only distilled or deionized water. Adding acid raises the density above design limits and damages the plates.
Acid burns from the sulfuric acid electrolyte and explosions from hydrogen gas released during charging. Protective equipment, an eyewash station and a ventilated charging area address both.
With correct charging and watering, most packs deliver about 1,000 to 1,500 cycles, which equals roughly three to five years of single-shift use. Deep discharge, overheating and missed maintenance shorten that life.
Lithium-ion is better for continuous multi-shift operation and low-maintenance requirements. Lead-acid is better for single-shift or double-shift duty with a low capital budget and trucks that need battery weight as ballast.
Check the level after every charge. Flooded batteries in daily use typically need water once a week, although frequency changes with temperature, charger settings and age.
Yes, in a designated area with adequate ventilation, no ignition sources and the vent caps left in place. The area should have an eyewash station and a clear route for exhaust air.
Charging heats the electrolyte. Placing a hot battery straight into service accelerates grid corrosion and water loss. About eight hours of rest lets the temperature settle before the next shift.
Return it to a licensed recycler. Lead, plastic and electrolyte are all recoverable, and lead-acid batteries have one of the highest recycling rates of any consumer or industrial product.
Send us your truck model, voltage, tray dimensions and shift pattern. Our engineers will return a matched specification, drawing and quotation.
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