Ten years ago, when a lift truck's battery started to lose its juice, there was only one thing to do: take it out and exchange it for a fresh one. Of course, you had—and still have—a wide array of options for carrying out the task. Depending on your operation (and budget), the choices ranged from manually operated overhead cranes or hoists that lift the 3,000-pound batteries into place to highly sophisticated automatic extractor systems that exchange batteries without human involvement.
But in the last few years, a rival technology has arrived on the scene. Known as "fast charging systems," these new devices can recharge batteries while they remain inside the vehicle, typically during breaks and other downtimes. The technology grew out of research originally conducted by the automotive industry to create battery systems for electric cars and buses. In the late 1990s, it was adapted for use by lift trucks and other vehicles used in distribution centers.
That's led to what could only be described as a power struggle in the battery industry, with two proven battery charging systems competing head to head. So far, neither method has achieved total market dominance, with customers deciding which way to go based more on their experience, preference and applications than on any inherent strengths or weaknesses in the two technologies. As a result, some users remain staunch advocates of battery exchange, and others are moving over to fast charging. Still others are adopting hybrid plans that call for exchanging the batteries that power their more heavily used vehicles and fast charging the others.
High rates of exchange
One company that uses traditional battery exchange systems extensively throughout its logistics network is K-Mart Corp. At the company's distribution facility in Lawrence, Kansas, for example, a single station supplied by MTC (Material Transportation Co.) charges batteries in three levels consisting of 110 positions. The Lawrence DC is a three-shift operation and runs a fleet of 139 electric vehicles that include conventional forklifts, pallet jacks, mine which batteries have reached the end of their useful life order pickers and turret trucks.
"The standard is that we have two batteries for nearly every truck, though we have three batteries for vehicles that [see] heavier use," says Mark Soetaert, director of maintenance operations. Soetaert says the facility uses MTC's EBatt system, which monitors battery usage and determines which battery should be used next. On average a battery will charge for eight hours, cool for eight hours and then power a vehicle for eight hours.
Most vehicles require one battery change per shift. When it's time for an exchange, a vehicle driver pulls up to the changer, where a battery maintenance worker scans bar codes on both the truck and the used battery. The system then instructs the worker where to place the used battery using a man-aboard transport mechanism. He deposits the battery and scans the location to confirm that he's put it in the correct charging slot. He is next instructed where to go to pull a fresh battery. He travels to that slot, scans the location and the battery, then pulls it and places it into the waiting vehicle. The entire process can be completed within minutes.
But the E-Batt system does much more than just manage the battery exchange process. It also provides K-Mart with detailed reports on battery usage, which help K-Mart determine which batteries have reached the end of their useful life (typically when the battery can no longer hold more than four hours' charge). Taking the poor-performing batteries out of the rotation cuts down on the number of exchanges, saves rack space, keeps trucks in work zones and frees up the chargers for powering high-performing batteries.
Good battery management isn't only about housekeeping, however. It can also save companies a lot of money. After it adopted a battery management system, a K-Mart facility in Illinois realized $250,000 in initial savings and continues to save $75,000 annually, says Jim Lane, vice president of sales for MTC. The facility was also able to reduce the number of spare batteries it kept on hand from 225 to 115.
One way management systems reduce costs is by taking the guesswork out of the battery retirement process. "There is a myth out there that people can run batteries that are eight years old and think they have good battery management even though the battery lasts only two hours and has to be changed often," says Tony Amato of Battery Handling Systems. He says some companies replace batteries by age, which is an imperfect indicator because some batteries are used more heavily than others. "The goal of any system," he says, "is to provide the power to run the truck throughout the shift."
Amato's company also makes exchange equipment and the computer monitoring systems that optimize battery usage. These systems charge the battery to correct levels, determine water needs and then select which battery should be used next. For operations with large lift-truck fleets, that automated battery tracking and rotation feature can be a big time-saver. Smaller operations, however, may not need sophisticated systems to manage battery rotation—for them, a display board is often all that's needed to track which battery has been charging the longest to ensure that the first battery in is the first battery out.
Make it fast
With fast-charging systems, by contrast, the question of which battery should be used next is not an issue. In fact, with fast charging, trips to the battery exchange room are eliminated altogether; instead, the trucks head to charging stations situated at various points within the distribution center where the batteries can be serviced without ever leaving the truck. "The idea is to recharge the battery while it's in the truck during break times," says Larry Hayashigawa, product manager for AeroVironment PosiCharge. "The system then charges the truck battery at a much higher rate than normal charging."
Typically, drivers travel to the charging stations, which are often located next to break rooms, just before taking their lunch or coffee break or right before a shift change. The drivers hook their truck batteries directly to the chargers until their break is completed. The fastcharging units deliver power to the batteries at three to five times the rate of traditional chargers, with units typically in the 400 to 600 amp range. These chargers also cost four to six times the price of conventional chargers, but they can make up some of their initial costs by eliminating battery change-outs, creating space where changing rooms had been, reducing the number of spare batteries needed and optimizing productivity by not taking drivers away from their work for battery exchanges.
"If you change a battery during the course of a shift, you're a candidate for fast charging," says Peter Michalski, vice president of Edison Minit-Charger.
Fast-charging batteries require additional cabling and larger connectors able to take the additional power load. These usually increase the price for these batteries by about 10 percent over conventional batteries. Many traditional batteries can be converted over for use as fast-charge batteries, but they may lose any existing warranties. Most major battery makers now produce batteries for fast-charging applications that include the larger connectors. Battery manufacturer Enersys, for instance, makes batteries with more copper to lower resistance and more lead to reduce heat buildup.
Even with fast charging, most users agree that at some point during the week, a battery needs to be restored to its full charge (fast chargers usually only partially recharge the batteries).That may be difficult for certain 24/7 operations. For these high-volume operations, a hybrid solution may be in order combining the two technologies so that fast-charged batteries are occasionally changed out to allow them to receive a full charge.
just add water
With all the debate swirling around battery recharging methods, it's easy to forget there's more to battery maintenance than just charging. Batteries also need to be cleaned, and they need to be watered. Batteries tend to lose water in the normal course of operations, causing electrolyte levels to drop. Low electrolyte levels can cause plates within the battery's cells to oxidize, which shortens the battery's life.
In the United States, most facilities top off their batteries with tap water, which can be delivered in one of two ways. If it's delivered via high-pressure flow, water is fed directly from a water pipe with pressure behind it. In operations that use the low-pressure flow alternative, the watering system will first feed water into a tank and then dispense it from there to batteries using gravity.
"You should have a system that can accommodate both high- and low-pressure flow as well as one that filters the water before it reaches the battery," notes Dagfinn Sivertsen, vice president of sales and marketing for Flow-Rite Controls. Sivertsen says many systems have small regulators on them to ensure that batteries do not overfill. They should be able to handle pressures up to 30 psi (most city water systems flow at about 20 psi) and gravity drops of six feet.
To get the water into batteries, some companies set up permanent stations with water supplies near battery exchange or charging points. Others use portable tanks on wheels to service batteries on the facility floor. Batteries should be watered at least once a week. Sivertsen suggests Wednesday as a good day to water ("W" for water and Wednesday). Avoid Mondays because, depending on the operation, batteries may have gone unused all weekend and may boil over easily.
