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Cordless tool makers battle over power

by Clair Urbain and Paul Arnold

Power tool manufacturers are battling over which is the best battery to power 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?

Available since 1998, some say the 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 recharging.

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 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 manufacturers of cordless tools 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."

Battling the cold?
Another point of contention is operating temperature.

Milwaukee Electric's Loferski and DeWalt's Rosenquist 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."

Panasonic's Bock admits the two cell formats react differently to cold temperatures, but calls the difference 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.

"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 issue
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.