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Flux Power Holdings Inc. makes lithium-ion battery packs designed for a number of applications including forklifts. Shown is the company’s 24-V Li-ion pack.

Lead-acid rules as forklift battery, but alternatives pursued

When it comes to electrification, forklifts are both ahead of the car market and behind it, and they are likely to stay that way for the near future.

They are ahead of passenger cars in that battery-powered forklifts already make up a significant share of the market. Ideal for indoor operations, they’re a necessity for certain environments, such as food-distribution centers. According to the Industrial Truck Association, electric forklifts’ market share has been rising over the past five years. Before 2007, electric forklifts captured about 52 to 56% of annual sales. Since 2008, the share has risen to between 59 and 65%.

Where the materials-handling market trails the car market is in the adoption of more advanced electrification technologies. Lead-acid batteries with a conventional charger are the predominant technology option, due to their low cost, reliability, and well-established supply chain. Nevertheless, the disadvantages of lead-acid batteries are leading some fleet operators to consider alternatives. Lead-acid batteries’ low energy density results in runtimes of no more than 5 to 6 h. Slow charge acceptance and the need to cool down after charging means extended downtime for recharging. Performance degrades as the state of charge drops. And lead-acid batteries have a low cycle life of about 200 deep cycles.

Cost comparisons

However, the materials-handling market is quite conservative and risk-averse. Warehouse operators need a reliable technology that will not prove challenging for forklift operators to use. They also need any new option to demonstrate a speedy return on investment (ROI), preferably in two to three years. Moreover, the advantages that some advanced electric technologies offer for passenger cars do not necessarily translate well to the forklift market.

Lithium-ion (Li-ion) batteries are one of the best examples of this. Their advantages in terms of energy density and durability are virtually insurmountable in the passenger car market. While the characteristics vary depending on the specific chemistry, Li-ion energy density ranges from around 90 to 120 W·h/kg, compared to 30 to 40 W·h/kg for lead-acid batteries. And Li-ion battery life cycles are 5 to 15 times longer.

However, Li-ion batteries need to come down in cost significantly to compete in this market. Although those costs are dropping rapidly, Navigant Research still estimates that cell costs are around $400-$700/kW·h, compared to $150-$400/kW·h for lead-acid batteries. In addition, materials handling is the rare market in which a Li-ion battery’s lower weight is a real disadvantage as the forklifts are designed around the weight of the lead-acid battery.

This is also an issue for fuel cells, but fuel-cell companies have worked closely with forklift OEMs to integrate their systems into existing forklift chassis. Like Li-ion batteries, fuel cells’ cost is a major inhibitor in this market. Ballard Power Systems, a primary supplier of proton exchange membrane (PEM) fuel-cell stacks for forklifts, estimates that a fuel-cell forklift module costs from $14,000 to $30,000, depending on the forklift size. By comparison, a lead-acid forklift battery costs between $2600 and $5500.

The advantage of fuel cells is that they can be refueled in minutes. This equates to a major productivity and cost improvement for warehouses with round-the-clock operations. With conventional lead-acid batteries, warehouses must have two spare batteries per forklift, and they need dedicated warehouse space for the batteries and charging facilities. In addition, the lead-acid batteries in these operations will last only around 3-4 years. These factors all add significant cost.

Fuel cells do require an investment in hydrogen infrastructure, which is why this market is still mainly concentrated on operators that can spread those costs across a large fleet. Nevertheless, fuel cells have captured a little over 1% of the annual U.S. forklift market in the past few years.

Niches for now

Fast chargers for lead-acid batteries have been available for industrial applications for more than a decade. Conventional chargers typically provide power at around 5 kW and can bring a battery at 20% state of charge (SOC) back to 100% SOC in around 8 h. Fast chargers range from 15 to 30 kW and can return a battery to full charge in just 1 to 2 h.

Often the fast charger is used to provide short bursts of opportunity charging. The forklift and the battery system require some modifications to allow a fast charge, which translates to slightly higher costs, and the charger itself is roughly four times the cost of a conventional charger, at around $8000. In addition, there are some operational issues, such as the need to return the battery to 100% charge periodically and the much higher power draw than with conventional charging. These characteristics have limited the potential customer base for fast chargers.

Overall, some fleet managers are sufficiently dissatisfied with current battery technology to be on the lookout for viable alternatives. For this reason, from 2014 to 2020, new technologies will continue to gain market share in the U.S., although conventional lead-acid will still account for the majority of the market.

Lisa Jerram, a senior research analyst contributing to Navigant Research’s Smart Transportation program, wrote this article for SAE Off-Highway Engineering. Information for the article comes from a Navigant report titled “Advanced Electric Forklift Technologies in North America” (

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