MRO Today - Cordless tools: Choose your weapon

Choose your weapon
What type of battery powers your cordless tools? Nickel-metal hydride cells promise longer run times. Nickel-cadmium cells declare longer cycle life and an ability to withstand the cold. Which is the better battery? Examine the issues.

by Paul V. Arnold and Clair D. Urbain

Cordless tools powered by nickel-metal hydride (Ni-MH) batteries look like a quantum leap in tool technology. With the promise of longer run times, maintenance and production workers like the idea of getting more work done before loading the battery pack back into the charger.

Available to manufacturing workers since 1998, some are convinced Ni-MH is the wave of the future. But others believe this techno-leap may not be such a big step.

The 3.0 amp-hour-rated Ni-MH cells offer longer run times than their 2.0 or 2.5 amp-hour-rated nickel-cadmium (Ni-Cd) counterparts. Amp-hours (Ah) is the rating for how long a battery will power a tool before it needs to be recharged.

Companies manufacturing tools powered by 3.0 Ah Ni-MH batteries tout run times up to 50 percent greater than tools powered by 2.0 Ah Ni-Cd batteries, and a 25 percent advantage when comparing 2.2 Ah Ni-MH batteries to 2.0 Ni-Cd cells.

However, some cordless tool makers believe Ni-MH cells have shorter cycle lives than the less expensive, more experienced Ni-Cd units on the market. It's a point of confusion that could cause some to shy away from the newer technology. Cycle life is the number of charge/discharge cycles a battery will go through before it fails.

DeWalt research shows that in controlled tests, Ni-MH batteries typically go through 250 to 500 charge/discharge cycles before failure. The company says today's Ni-Cds offer nearly twice that.

"We are seeing Ni-MH power tools in the field costing more than Ni-Cd power tools, but workers are getting as little as a quarter of the cycle life from the batteries when compared with Ni-Cds," says Pete Rosenquist, senior product manager for cordless tools at DeWalt.

Others cite similar findings.

"It is true that Ni-MH cells will run a tool longer between charges, but we've seen the number of times that battery can be charged is considerably less than a Ni-Cd battery," says E.J. Loferski, cordless tool product manager at Milwaukee Electric Tool.

In its tests, Ni-MH cells racked up 400 to 500 charges, compared to 800 for Ni-Cd cells. Both DeWalt and Milwaukee Electric currently sell only tools powered by Ni-Cd cells, but Milwaukee plans to offer accessory Ni-MH batteries in the near future.

Other cordless tool manufacturers see few, if any, weaknesses in Ni-MH.

Ken Hefley, vice president of marketing for Makita, a pioneer in the Ni-MH-powered tool market, calls the cycle life difference between the two formats "minimal, at best."

"We claim that the charged cycle life difference between 2.0 Ah Ni-Cd and 2.2 Ah Ni-MH is less than 10 percent," he says. "At the same time, the 2.2 Ah Ni-MH exhibits 25 percent more capacity. The offsetting gain in capacity against the margin loss in cycle life equates to 13 percent more lifetime work for the battery. That's why Makita is sold on Ni-MH."

Doug Bock, national sales manager at Panasonic, which makes cordless tools with Ni-MH and Ni-Cd cells as well as supplies Ni-Cd and Ni-MH cells to a variety of tool manufacturers, says Ni-MH cells, when charged correctly, last as long as Ni-Cd cells.

"The charger is the key ingredient," he says. "Our battery charger fully charges the Ni-MH battery each time. The cycle life is approximately 1,200 times, which is consistent with Ni-Cd cycle life."

Batting the cold?
Another point of contention is operating temperature. DeWalt's Rosenquist and Milwaukee Electric's Loferski state Ni-MH batteries have a narrower operating temperature when compared with Ni-Cd batteries. Loferski estimates Ni-MH batteries work best between 40 and 105 degrees F.

"We have seen power drop severely under 40 F," he says. "When the battery temperature is at freezing or below, Ni-MH batteries won't work at all, where Ni-Cd batteries will put out power at temperatures as low as 0 F."

While few manufacturing plant applications occur in temperatures below 40 F, such claims can give Ni-MH a reputation of being less robust than Ni-Cd.

While admitting the two cell formats react differently to cold temperatures, Panasonic's Bock says the difference is a non-issue.

"It's a chemical fact that power from Ni-MH cells will drop off at lower temperatures," he says. "However, we have been marketing the technology for almost one year now and our experience with units in the field is that perceptible power loss at lower temperatures has not been an issue."

Makita's Hefley takes Bock's comments a step further. While admitting a cold temperature problem did exist in the battery's early testing stages, Hefley says those problems were eliminated before his company put a Ni-MH-powered product on the market.

"We have a patented process that conditions each battery before it leaves the factory," he says. "The battery will withstand and endure all cold temperature applications in the market today."

Makita used an unconventional test recently to prove its case. Please do not try this test at home.

"We submersed a Ni-MH battery in a bucket of water, froze it solid as a rock, took a device to crack the battery out of the ice, and then plugged it into a drill and ran screws with it," says Hefley.

Environmental friend or foe?
Concern for the environment is one of the most compelling reasons for selecting Ni-MH over Ni-Cd.

Ni-Cd cells contain cadmium, a toxic heavy metal that shouldn't be discarded in sanitary landfills. These cells can be recycled, though, and more recycling centers are accepting these batteries than in the past.

Ni-MH cells don't have disposal issues. They aren't toxic, so they can be discarded in normal trash.

Is cost a concern?
Milwaukee Electric Tool and DeWalt cite that initial cost of Ni-MH tools is higher than Ni-Cd tools. Combine that with their argument that the batteries don't last as long, and they make a compelling case to stick with Ni-Cd-powered tools.

"Panasonic has been selling Ni-MH-powered tools for 10 months, and they have been as much as 30 percent more expensive than Ni-Cd units," says Bock.

Says Hefley: "You're going to pay a higher price for a better product."

But, as with any high-tech device, the price margin narrows over time. Panasonic recently introduced a line of drill/drivers and a hammer drill powered by Ni-MH cells that cost the same as its Ni-Cd versions.

Looking to the future
While the current battery market focuses on the nickel-cadmium and nickel-metal hydride formats, it is also important to look into the future. The future of portable power may be as close as your cell phone or laptop computer.

"Nickel-metal hydride got its start with those products, and they give you a glimpse of what could power cordless tools in the future," says Dave De Vries, a power tool product manager for Energizer. "Lithium ion is a battery technology that is starting to be used in cell phones. It's possible you'll see lithium ion in some sort of power tool in the next five years. It's very good technology. It's at the stage of development that Ni-MH was five years ago."

This article appeared in the February/March 2000 issue of MRO Today magazine. Copyright 2000.