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Operators of forklifts and warehouse executives don’t need me telling them about the importance of the battery. To put it simply, the battery is the heart of the forklift and how well it performs will determine how much downtime the forklift will experience.
There are five types of batteries –- nickel cadmium, nickel-metal hydride, lead acid, lithium ion and lithium ion polymer.
Up until now the battery that has been used most consistently to power forklifts is the lead acid battery. It is one of the most economical batteries around, it is recyclable, it has been around since 1859 so people are familiar with it, it is maintenance free and can operate in any configuration, it has no memory so it can remain on float charge for a long period of time without being damaged, it has low self-discharge and yet is capable of high discharge rates.
However, it has its limitations, too. For example, it cannot be stored in a discharged condition, it has poor weight-to-energy density that limits its use to stationary or wheeled applications, it offers a limited number of full discharge cycles, it is environmentally unfriendly because the electrolyte and lead in it can cause environmental damage and there are concerns that the battery will leak if involved in an accident, and thermal runaway can occur if the battery is not properly charged.
In recent years lithium-ion batteries have been used to power forklifts. Some think it is a better alternative to power forklifts than the lead acid battery. The people that favor lithium-ion batteries argue that it carries a charge longer and delivers more continuous performance than a lead acid battery. Those who favor the lithium-ion battery also say that it offers longer run-time and shorter charge time so it reduces the long-term cost of ownership over the lead-acid battery and it requires very little maintenance.
However, it too has its limitations. For example, it needs circuit protection, it is subject to aging even if it is not used, it offers a moderate discharge current, it is subject to transportation regulatory controls, it is expensive to manufacture, and it is not mature.
During tests the battery can experience changes in metal and chemical combinations. Moreover, it costs 40 percent more to manufacture than nickel cadmium (NiCd) batteries.
Advocates of the NiCd battery prefer its fast charge to slow charge and pulse charge to DC charge. It is ideal for heavy-duty applications and needs to be worked hard because it performs best if it goes through a periodic full discharge so that large crystals won’t form on the cell plates. If the crystals are allowed to develop, this battery could gradually lose its performance.
Its limitations include the fact that it contains toxic metals that can damage the environment. As a result, some countries limit its use. Moreover, it has a high self-discharge so it requires recharging after storage.
The nickel-metal hydride (NiMH) battery was originally developed in the 1970s as a way to store hydrogen. It is mostly used to power satellites. This battery is bulky and includes high-pressure steel canisters and it costs thousands of dollars per cell. Its advantages include high energy density and it features environmentally favorable metals. It offers up to 40 percent higher energy density then the NiCd battery. It is less durable than the NiCd. If it is cycled under heavy load or stored at high temperature its service life is reduced. It suffers from high self-discharge that is noticeably more than that of the NiCd.
It is less prone to memory issues than the NiCd so periodic exercise cycles are less required and there are no regulatory controls concerning its storage and transportation. It is environmentally friendly and contains only mild toxins. It can be recycled.
Limitations include limited service life. If it is repeatedly deep cycled, especially at high load currents, the performance deteriorates after 200 to 300 cycles. It is capable of offering high discharge current. However, repeated discharges with high load currents reduce its cycle life. It produces heat during charging and requires more time to charge than the NiCd. It experiences about 50 percent higher self-discharge than the NiCd. It is high maintenance and needs regular full discharge to prevent crystalline formation. It is about 20 percent more expensive than NiCd.