Filling a forklift battery with water

The type of forklift battery water you use is very important, get it wrong and you can significantly reduce the batteries life, which can cost you £1000’s in replacing the battery, and even more in reduced productivity.

Note: This article focuses on water for flooded lead-acid forklift truck traction batteries.

The “water” in the forklift battery is called electrolyte and is actually a mixture of sulfuric acid and water. During charging the battery heats up and some of the water will leave the battery cell through evaporation. In addition, though a process called electrolysis the water breaks down into hydrogen and oxygen gases, which float out of the cell. Overtime this reduces the electrolyte level in the battery, and the water will need replacing with either deionized water or distilled water.

If the electrolyte level gets too low, then the plates in the battery cells can become exposed which causes damage. In addition, the sulphuric acid becomes more concentrated.

It is important to use the correct type and quality of water for forklift truck batteries. Mains water from your tap contains impurities that can cause damage to the battery. During discharge of the battery the impurities attach themselves to the plates inside the battery cells. Over time this builds up into a crust type of layer, this reduces the active surface area of the cell plates with the effect of reducing the batteries capacity.

This build-up of impurities can have a devastating impact on the capacity of the forklift battery and therefore the amount of operational time between chargers and its life expectancy.

To avoid this from happening it is important to use water where the impurities have been removed.

forklift battery maintenance is needed due to water loss through electrolysis
Forklift Battery Water Loss

| Forklift Battery Maintenance Water

Forklift battery water can be produced in 2 main ways:

  1. Distilled Water
  2. Deionized Water

The most common type of water for forklift batteries is deionized water, see below for more details.

Both methods remove the dissolved solids from the water. Please note that filtration alone will not do this. Filters are designed to remove suspended particles from the water and not dissolved solids.

Deionized Water System – Single PS-300

Rated 5.00 out of 5
( 1 review )
£269.00 Price incl. VAT: £322.80

Distilled water for forklift batteries

Water Distillation
Water Distillation

Distillation is the process where the water in a container is heated until it evaporates and becomes vapour. In a separate container the vapour is cooled back into water. Any impurities that were in the original water are left behind in the first container, resulting in purified water in the second container.


Pros: Distilled water is very pure as any impurities that do not boil, which will be the vast majority, will be left behind.

Cons: It is an expensive process and one that is out of reach for most people whose requirements are relatively small. The production is normally reserved for industrial applications that require vast amounts of purified water. Water distillation is also very energy intensive.

Deionized water for forklift batteries

Deionized, sometimes called demineralised water, is produced by passing water through ion-exchange resins. The resin is made up of cationic and anionic beads. As the water passes through, the dissolved solids in the water are electrostatically attracted to the resin beads and “stick” to them, removing them from the water.


Pros: Deionised water is also very pure water, like distilled water, but at a fraction of the cost and significantly quicker. It is also very easy to produce on site.

Cons: May not remove certain organic molecules, such as viruses and bacteria, which means it isnt always suitable for applications involving food production. But completely safe for lead acid forklift battery water.


The most cost-effective and simplest way to produce forklift battery maintenance water on site is with a deionized water system. After the initial purchase and installation of the system, replacement cartridges are bought, which are quick and easy to fit and don’t require any special skills or tools.

Another option is to buy deionized water, but as water is heavy the cost of posting to your facility is often very high, but if your demand is very low then this can be a viable option. The contained water will only have a certain shelf life as it can absorb impurities from the container and the air.

| How do you add water to a forklift battery?

You now know the importance of adding water to your forklift battery, check out our next article on forklift  battery maintenance. Covers all of the main points and will answer your questions.

| Related Guides

| Related Products

Deionized Water System – Single PS-300

Rated 5.00 out of 5
( 1 review )
£269.00 Price incl. VAT: £322.80

Deionized Pure Water System – Double PS-400

Rated 5.00 out of 5
( 1 review )
£587.00 Price incl. VAT: £704.40

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