Batteries: The Power Behind the Tool

Manufacturers of cordless power tools offer insights to help managers specify the right batteries and charging technology

By Dan Hounsell  

Buying a cordless power tool involves researching and understanding a range of important factors, and one of the most overlooked elements of the buying decision involves the batteries that provides the tools’ power. Managers specifying cordless tools spend more time researching other aspects of cordless power tools and too little time checking out batteries and charging technology, say tool manufacturers.

Maintenance and engineering managers who do look closely at battery and battery-charging technology will find noticeable advances in these products in recent years. While issues such as durability, ergonomics and weight are essential in finding the right tool for the job, paying more attention to batteries and chargers also is apt to pay off in terms of cost, reliability and performance.

Inside Batteries

The major challenge for power tool manufacturers is developing batteries that can deliver required power output cost-effectively and reliably.

“Power tools are the hardest customers on batteries,” says Christine Potter, product manager for cordless tools for DeWalt Power Tools. “They require a lot of power.”

The demand for more powerful cordless tools is certain to continue, given the tools’ popularity. From all types of drills and drivers to the entire family of saws and beyond, every corded tool today seems to have a cordless counterpart, and more are on the way.

One noticeable change from early-generation cordless tools is the advance in voltages. Early batteries delivered 6 volts, while today’s tools offer up to 24 volts for heavy-duty uses.

Two types of batteries — nickel cadmium (NiCd) and nickel metal hydride (NiMH) — remain the dominant options for today’s cordless tools. Though NiMH technology has made some inroads in recent years, most manufacturers still design the bulk of their tools to operate on NiCd batteries.

“It’s amazing how many cordless tools run on NiCd batteries,” says Paul Papineau, cordless tool marketing manager for Hilti Inc. NiCd remains popular largely because of cost and performance advantages.

“NiCd is still the gold standard in battery performance,” says John Sara of Milwaukee Electric Tool Corp. “NiCd battery packs under normal conditions can reach 600-800 cycles of full recharge before they reach the end of their life. NiMH packs have only half the cycle life of NiCd packs.”

While today’s NiCd batteries are a bit smaller and lighter than those of a generation ago, advances in NiCd technology have slowed somewhat in recent years, manufacturers say. Perhaps the biggest recent advance for these batteries is the improvement in amp hours, which quantifies the amount of operating capacity a battery has when fully charged.

The higher the rating, the longer the tool can operate before needing to be recharged. Today’s batteries have amp-hour ratings in 1.2 up to as high as 3.5, and that kind of performance tends to matter most to tool users.

“Time is money, and no one wants to stop in the middle of a job to get another battery pack back at the truck,” Sara says.

NiMH batteries remain a viable option for many tool users, but a number of factors are holding them back from wider acceptance by manufacturers and tool specifiers.

Specifically, NiMH batteries offer half the cycle life as NiCd batteries, and their performance tends to lag in lower temperatures, Potter says.

“Since professional end users don’t stop working from November to February, they need a pack that can provide the most output as temperatures decline,” Sara says. “Also, NiMH costs significantly more.”

While no new alternatives to these two battery types are on the horizon, manufacturers are watching for any battery chemistries that might provide benefits beyond the existing options.

For example, lithium batteries that are used to power watches, laptop computers and cell phones are attractive to cordless tool manufacturers because they are smaller and lighter than NiCd and NiMH, Papineau says. But at this point, lithium chemistry simply can’t provide enough power to meet the power output of cordless power tool users.

“It’s still a couple of years off,” says Steve Cole, associate product manager for Bosch Power Tools. “It’s still too new, and they have some major shortcomings.” Nonetheless, manufacturers will keep looking for sources of greater battery power because tool users continue to demand it.

Says Papineau, “They want something the size of a watch battery that has the power output of a tractor battery.”

Smart, and Getting Smarter

While advances in battery technology might have slowed in recent years, the systems that recharge batteries have made great strides. Managers now have options not available five years ago that can greatly enhance the performance life of batteries and, in turn, the productivity of staffs that use them.

Some battery-charging systems use either heat or time to charge batteries, but these criteria don’t maximize battery performance life and, in fact, can harm it.

“Heat kills batteries, and additional heat should be avoided when possible,” Sara says. To avoid problems created by too much heat during charging, manufacturers developed smart-charging technology, which they continue to refine.

“Our chargers have a built-in sensor that prevents packs that are too hot from being charged, which could result in damaged battery cells,” Sara says. “Once the pack reaches the appropriate charging temperature, the charger automatically begins to charge the pack.”

Today, managers can get systems that recharge batteries in anywhere from five hours to as little as 15 minutes. Systems that recharge batteries in a shorter amount of time are better for the battery, Cole says, adding that the 15-minute charger uses fuzzy logic to monitor battery cell characteristics and charge each cell in a battery to the proper level. Most tool users, however, don’t need that kind of recharge speed.

“For most people, a one-hour charger is the best,” he says.

Finding the Right System

Managers in the market for cordless power tools have a tendency to focus too much on a tool’s power and err on the side of too much — a higher-voltage battery — rather than giving workers too little. But manufacturers say that in doing so, they might actually make workers less productive.

The first step in this process of matching tools to user needs involves determining as accurately as possible the way in which a worker will use a particular tool.

“If a guy is installing locks and door hardware all day, he might need an 18- or 24-volt battery,” Cole says. “But if he’s only shooting a few screws into wood, a 12-volt or a 14.4-volt battery might be enough.”

Additionally, higher-voltage batteries tend to be heavier and larger. As a result, specifying them for users who don’t need the power also can make the tools unnecessarily heavy and unable to reach into some areas where work needs to be done.

Sara says managers will need to determine whether run time or the weight and size of the tool is the top consideration.

“Higher voltage and amp hours will provide more power and run time, as well as some additional weight,” he says.

Adds Cole, “The cost of the product is 50-75 percent for the battery. If you don’t need a 24-volt drill, don’t buy it because in large part, you’re paying for the bigger battery.”

Battery decisions also can affect tool purchasing in another important way. The option to buy a tool package — for example, a drill, a saw, a battery charger and two batteries — at a reduced price seems to offer the buyer a good deal, Papineau says. The buyer gets two tools and a battery for each tool for a lower price.

But if workers will use both of the tools simultaneously, each tool will require a battery and a spare, and the manager will be forced to buy two more batteries, he says. And because of the high cost of batteries, this arrangement actually might end up costing as much in the long run as buying the needed tools and batteries in the first place.

Finally, in this age of growing environmental awareness, managers should understand the recycling and disposal requirements related to batteries before purchase. NiCd batteries must be recycled, while NiMH do not need to be at this time, Sara says. Most power tool retailers, manufacturers and distributors have information on battery collection and pickup options available to facilities.

Battery Myths & Misconceptions

Manufacturers of cordless power tools are well aware that customers have some unfounded beliefs when it comes to batteries. Two myths generally top the list.

First, many users believe that leaving a battery on a charger indefinitely will never harm it and will keep it ready to use.

In fact, tool manufacturers recommend that users avoid leaving batteries on chargers around the clock.

“Users tend to think that doing this is simpler,” says Paul Papineau, marketing manager for Hilti. “They think that when they need to use it, it’ll be fully charged and ready to go.”

If a tool is used regularly, leaving it on the charger overnight isn’t a problem. But simply leaving it on the charger for days on end can damage the battery.

Second, many users believe that a battery has a “memory” created by repeatedly using it and recharging it at the same levels. They believe that completely draining and discharging a battery will enable it to hold a charge longer and perform better.

“That might have been true for batteries five or six years ago, but memory doesn’t exist for batteries today,” says Steve Cole, associate product manager for Bosch Power Tools.

Completely draining a battery by, for example, taping down a tool’s trigger can damage the battery’s cells and prevent them from accepting a full charge, says Christine Potter, product manager for cordless tools for DeWalt Power Tools.

“Don’t tape down the trigger,” Potter says. Instead, users should heed changes in tool performance.

"To get the maximum life out of a battery, you should recharge it as soon as the tool begins to have difficulty doing the job,” says John Sara of Milwaukee Electric Tools.

— Dan Hounsell

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  posted on 7/1/2003   Article Use Policy

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