operator disconnecting a forklift battery before charging it

The performance of your forklift battery directly impacts on the performance of the forklift and your entire operation. A poor performing battery will hold less charge and need charging more frequently, which is less time the truck can be in operation. You may end up having to have a second battery or even a second truck, just to ensure you have the availability your site demands. In addition you will be spending more on electricity to charge it and it will require more frequent maintenance.

This guide aims to cover how charging a forklift battery effects it performance and life. This guide focuses on flooded lead acid, but many of the points are valid whatever the tech.

| Expected Life of a Forklift Battery

The life of a forklift battery is measured in charge cycles. A charge cycle being 1 discharge followed by full recharge. Manufacturers are today building forklift batteries to last 1,500 charge cycles. The 1,500 cycles is based on correct usage and the battery being well maintained. In the end like any other piece of equipment a forklift battery will fail prematurely if it is abused and misused!

For the average business the forklift will only be lightly used and may only need the battery to be charged once per week. In such cases the forklift battery will last 10’s of years if correctly maintained. Buy even heavy use applications should expect the 1,500 cycles to last 5+ years.

| When should a forklift battery be charged?

A deep cycle lead acid forklift battery should be discharged to 80% of its rated capacity before being put on charge. It is still common practise that a battery is charged by a routine at set times of the day or week, rather than when it is 80% discharged. By doing this you are prematurely using the charge cycles of the battery and therefor reducing its operational life.

In certain operations it may be necessary to ensure a battery is fully charged at certain points of the day, so the battery is not fully discharged before being charged. In these instances the operational benefits have to be measured against the fact that the battery will need to be replaced sooner.

It is also bad practise to leave forklift batteries sat for long periods of time, especially when they are discharged. This again will cause sulfation of the plates in the cell.

forklift battery charging - Forklift truck preparing for the battery to be charged
Forklift Battery Charging

| Correct Charger

It is important to ensure that the battery and charger are correctly matched. Simply if you have a battery capacity of 500 amp-hours (Ah) and a charger with a rated output of 50Ah, then you can expect it to take 10 hours to fully recharge the battery (500/50=10). It is normal to have a charger rated to charge a specific battery in 8 hours.

If you use a over rated charger then the battery will charge too quick and generate excessive heat due to this. This will quickly cause irreversible damage to the battery and it will also require more frequent maintenance.

Using an under rated charger and the battery may never receive a full charge which will result in sulfated cell plates and a subsequent reduced capacity. In addition the battery will also become unequalized, causing further issues (see below).

| Overcharging

Overcharging of a forklift battery occurs when the battery receives a greater amount of energy that it was designed to accept. This excessive energy results in high battery temperatures and excessive gassing. Ultimately shortening the life of the battery.

| Opportunity Charging

As the name suggests, opportunity charging of a forklift battery is when the battery is charged for short periods as opportunities arise. Typically this is during breaks in the work such as meal times or a change of shift. Individual occurrences of opportunity charging is not an issue, and in some applications can help with productivity. But if conducted repeatedly over prolonged periods without adequately fully charging or equalising the battery, then the battery will become sulfated and capacity will be lost.

| Equalization Charge

During an equalization charge the battery is deliberately overcharged by approximately 10%. An equalization charge does 1 things:

  1. Removes the sulfate crystals from the cell plates.
  2. “mixes” the acid, preventing it from becoming stratified.

Many charges have a charge setting for equalization. You would need to keep a record of when you carry these out and follow the manufacturers guidelines on advised frequency.

Some charges provide an equalization charge on a set frequency, for example every 7th charge. Charges with this included are “set and forget”.

As the battery is being overcharged during equalisation, it will be hotter and gas more than normal.

| Temperature

Hot and cold temperatures greatly effect the performance of forklift batteries. The electrical power in a battery is produced through chemical reactions, and all chemical reactions speed up the warmer they are and slow down the colder they get. With each 10 ͦ c (50 ͦf) increase/decrease in temperature, the chemical reactions /double/half.

So batteries operating in hot conditions will fail sooner.

Batteries in cold applications (such as cold storage units) will have significantly reduced capacity and require charging more frequently.

Obviously the biggest causes of increased ambient temperature is the weather! And there isn’t a lot we can do about that!

How the battery is charged and rested can have a marked effect on the battery temperature. The forklift batteries temperature will be the hottest during charge, and will take some time to cool down once the charge is completed. It was previously the rule of thumb that the battery should charge for 8 hours and rest for 8 hours! But in practise, with modern charges, 2-4 hours should be sufficient.

Battery manufacturers base the predicted performance and life calculations on a battery temperature of around 25 ͦc (77 ͦ f).

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