why is there crust around a forklift battery

The Anatomy of the "Crust"

In the material handling world, that white or grayish-green fuzzy buildup on forklift battery terminals and casings isn't just "dirt." It is primarily the result of a chemical reaction between the battery’s internal electrolyte and the external environment.

Specifically, it is usually one of two things:

Lead Sulfate ($PbSO_4$): The result of the discharge cycle.

Anhydrous Aluminum Sulfate or Copper Sulfate: If the acid has begun eating the terminals or cables.

1. The Chemistry of Electrolyte "Creep"

The lifeblood of a forklift battery is Sulfuric Acid ($H_2SO_4$) diluted in water. Ideally, this stays inside the cell. However, batteries are not hermetically sealed; they need to breathe.

Capillary Action

Through a process called "electrolyte creep," the acid moves up the battery posts or through microscopic gaps in the plastic casing seals. Acid has a high surface tension and "climbs" toward the terminals. Once it hits the air, the water evaporates, leaving behind a concentrated acidic residue that reacts with the metal of the terminals.

The Overwatering Culprit

This is the most common "human" cause. If a battery is topped off with water before it is charged, the electrolyte levels will rise as the battery heats up and gasses during the charge cycle. This leads to an "overflow" or "boil-over."

The acid spills onto the top of the battery.

The water evaporates.

A conductive path of white crust (dried acid and sulfates) forms across the top of the battery.

2. The Gassing Process (Electrolysis)

When a forklift battery charges, it undergoes electrolysis. The water in the electrolyte is split into Hydrogen and Oxygen gases.

$$2H_2O \rightarrow 2H_2 + O_2$$

As these gas bubbles rise to the surface, they create a fine acid mist. This mist escapes through the vent caps and settles on the battery's surface. Over hundreds of charge cycles, this mist accumulates, reacts with the lead or copper connectors, and crystallizes into the "crust" you see.

3. Why the Crust is Dangerous

It’s easy to dismiss the buildup as an aesthetic issue, but in industrial applications, it is a silent killer of productivity.

Parasitic Draw (The "Tracking" Effect)

The crust is often acidic and damp. This creates a conductive path between the positive and negative terminals. Even when the forklift is turned off, the battery is slowly discharging across its own lid. This is known as Tracking. It can lead to:

Unexplained "dead" batteries in the morning.

Heat buildup on the battery casing.

Blown fuses or damaged controllers in the forklift.

Terminal Resistance

When the crust forms between the lead post and the cable connector, it introduces Electrical Resistance.

According to Ohm’s Law ($V = I \times R$), increased resistance causes a voltage drop.

The battery might have plenty of "juice," but the resistance at the terminal prevents that power from reaching the motor.

This generates heat, which can eventually melt the lead posts entirely.

4. Prevention and Maintenance

To stop the "science project" from growing on your battery, a strict maintenance protocol is required:

The Verdict

The crust is a physical manifestation of acid migration. Whether caused by the natural "breathing" of the battery during electrolysis or sloppy watering habits, it represents a breakdown in the containment of the sulfuric acid. Left unchecked, it will eat your cables, drain your capacity, and eventually "weld" your connectors to the battery.