Lithium-ion lowdown

As the dust settles from Li-ion cordless tool introductions, the battle begins for your tool dollar.

by Clair Urbain

As lithium-ion (Li-ion) cordless tools flood sales floors and jump out at you from magazine ads, catalogs and sales flyers the next few months, you can’t help but be at least a bit curious about them.

A common theme runs through manufacturer claims. First, Li-ion batteries, volt for volt, weigh 40 percent less than nickel cadmium (Ni-Cd) batteries. Second, they offer up to 2.5 times more run time than our old friends, the Ni-Cd or nickel metal hydride (NiMH) cells.

You’ll find refinements in the new tools as well, taking the man-machine interface to even higher ergonomic levels. The tools also have advanced electronics to manage the tool and recharging tasks.

But with the improvement in weight, power and run time, there is a cost: They cost as much as 50 percent more than Ni-Cd tools.

Li-ion technology
According to battery experts, Li-ion batteries pack high energy in a tiny package. That’s what makes them a good choice for devices such as laptops and cell phones and, most recently, power tools.

It’s not new technology. Non-rechargeable lithium-based batteries have been around since the ’70s, and are a common power source for watch batteries. Rechargeable Li-ion batteries were first commercialized by Sony in 1991 as a superior alternative to Ni-Cd cells.

The battery experts also claim that every technology has its Achilles heel. With lithium, it is inherently unstable during charging. That’s why the new Li-ion tools boast improved electronics systems to charge and discharge the cells efficiently and reliably.

In power tools, Li-ion batteries run differently than Ni-Cd or NiMH batteries. Users will notice that on top of more power and longer run times in a smaller, lighter package, the power in some brands hangs in there until it’s almost totally discharged. It’s a function of the electronics some models use.

Dramatic weight loss
It’s interesting to see how the power tool companies have leveraged the 40 percent battery weight loss. It has resulted in a splintering of voltages that are better matched to the types of jobs at hand.

“Over the past 20 years, the market has gone from 9.6 volts to 36 volts and then fell back into an 18-volt Ni-Cd platform because it proved to be the best combination of power and weight for most cordless applications,” says Ken Hefly, senior vice-president of Makita USA, which introduced its LXT 18-volt Li-ion tools in late 2005.

“The 36- and 24-volt Ni-Cd tools were too bulky for users, which reinforced 18-volt performance. The 18-volt power-to-weight ratio was optimum for the technology at hand. With Li-ion technology, Makita and Sony researchers developed a complete system in a tool as compact and light as a 12-volt driver-drill but as powerful as a best-in-class professional 18-volt driver-drill,” says Hefly.

Milwaukee launched its V28 28-volt Li-ion line in early 2005. This year, it’s adding a V18 18-volt battery, which can be used with any tool in Milwaukee’s 18-volt line.

DeWalt and Bosch pushed their Li-ion technology and recently introduced 36-volt systems.

DeWalt’s system uses nano-phosphate technology developed by MIT researchers and licensed by A123 in a line of tools that sources claim to be as powerful as corded tools.

Bosch builds off of its Litheon advanced Li-ion technology in two directions, taking advantage of the weight savings and greater power with 36- and 10.8-volt tool lines.

The 36-volt line begins with its 1" SDS Plus Bulldog rotary hammer that it has already introduced and field-proven in Europe. At the other end of the scale, it has developed two smaller, yet powerful 10.8-volt drivers that Bosch sources report can complete 80 percent of the tasks that tradesmen face. Bosch will introduce a 36-volt drill-driver, hammer drill-driver, circular saw, recip saw in late 2006.

More power, greater performance
Generally, at the higher voltages, users can expect about twice the run time with Li-ion cells when compared with 18-volt tools. It de­pends on the tool and application.

“We asked end-users what they wanted, and they desired a cordless tool that will work all morning on one battery, then on another battery in the afternoon. We expected 20- and 24-volt cells to meet their needs, but that voltage didn’t hit the power or speed needs of users,” says Christine Potter, senior product manager of the Industrial Products Group at DeWalt.

This new class of power tools fulfills on that promise, according to data provided by the power tool companies, and it comes from the increased voltage ratings, Potter says. “The more power and more run time is solely due to higher voltage, not the Li-ion technology.”

DeWalt claims its drill-driver can make 70 2 3/8"-diameter holes on one charge; Milwaukee sources say you get 218 cuts of 1" conduit with its V28 portable band saw; and Bosch claims its 10.8-volt pocket driver can run in 100 3" #8 screws without switching batteries.

“Li-ion cells hold more power in the same size package or the same power in a smaller package. A 36-volt Li-ion battery is about the same size as an 18-volt Ni-Cd, but has twice the power; a 10.8-volt Li-ion battery has comparable power to a 9.6-volt Ni-Cd equivalent but is less than half the size,” says Edwin Bender, Litheon cordless tool product manager at Bosch Power Tools and Accessories.

Cycle life confusion
Perhaps the area of the most controversy in the new world of Li-ion technology revolves around cycle life, or the number of times Li-ion batteries can be recharged before failure. It’s a topic whispered at trade shows and strategic marketing meetings, because cycle life ultimately affects the total operating cost of the tool.

Milwaukee claims it has a 3X battery life when compared with 18-volt Ni-Cd batteries in high amp-draw applications. Multiply that by the ability to do twice the work between charges and, theoretically, you can expect 6X the work from the new V Technology batteries.

DeWalt claims its new battery system can achieve 2,000 charging cycles, while other battery formulations it considered lasted 600 charging cycles. Metabo claims up to 1,500 charging cycles before failure.

Bosch sources reports its Litheon cells are designed in a way that it can reach up to five times the service life of current competition.

Each manufacturer has its own spin on battery life. To get an apples-to-apples comparison, inquire about each tool in the same application.

Battery and charging technology
The more sophisticated batteries require smarter battery chargers to assure correct and efficient charging. Metabo recently introduced an 18-volt “li-power” Li-ion battery pack that can be used on its present tools. In addition to its favorable weight-to-power ratio, Metabo sources report its charging system uses a patented air cooling method that charges batteries fast, yet allows them to last as much as twice as long as Ni-Cd or NiMH cells. The battery packs also have a display that shows overload warning, temperature monitoring, battery capacity monitor, and low capacity warning. Internal circuitry monitors charging temperature and load for 30 percent faster charging.

Milwaukee opted to put a fuel gauge on the battery pack so users know how much power they have at hand for the immediate task. The Performance Optimizing Circuit in the battery pack balances cell charging and discharging, and can be connected to a monitor for readouts on use, abuse and other battery-critical issues. Makita’s charging system is capable of similar readouts.

DeWalt’s fuel gauge is on the charger, not on the battery. The battery will fully charge in one hour.

Bosch Litheon chargers and battery packs are designed to dissipate heat through a ribbed shell and specially designed vents. Electronic Cell Protection (ECP) manages the flow of energy and the charge and discharge cycles to dramatically extend cycle life. The one-hour chargers on the 36-volt tools can be 80 percent charged in 30 minutes.

Different approaches
“When it comes to lithium-ion technology, some manufacturers are using similar battery chemistries, but that’s where the similarity ends,” says Bender, “The manufacturer must design the tool and battery to properly manage energy flow while taking into account performance, cycle life and cost. This total package will be the ultimate differentiator for this new generation of tools.”

Learn more about Li-ion tools
A brief product comparison chart and links to power tool company Web sites
 

Published in the March/April 2006 issue of Contractor Tools and Supplies magazine.

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