Cordless tools do more and do it better every year. Their gearing becomes more efficient, materials get lighter and stronger, and ergonomics improve. Recently, optimizing battery performance has taken center stage in cordless tool development. Manufacturers want to increase batteries' cycle lives; they also want to increase run time per charge, which enhances tool performance in the field.

Emerging Technology

The biggest ripple in the cordless tool pond right now is the burgeoning use of nickel metal hydride (NiMH) battery chemistry. The standard to date, of course, is nickel cadmium (Nicad). Significant differences between the two battery chemistries affect their performance, life cycles, and run times. They also fuel a lot of varying opinions about which technology will lead the next era in cordless tool development.

NiMH the relative newcomer, is grabbing tool engineers' attention because it exhibits longer run times per charge than Nicad does. A NiMH battery stores more of the chemicals and materials that generate direct current, so it produces more amp-hours than a Nicad pack of equivalent volume does. NiMH batteries can work longer between charges. They're also lighter than their Nicad equivalents and are said to be less harmful to the environment if they're dumped into the waste stream.

Makita, Milwaukee, and Panasonic say the future of cordless power tools lies in NiMH technology. So why haven't all the cordless tool manufacturers made the leap to NiMH? Actually, many European toolmakers have. European consumers and legislators are generally much more sensitive to environmental issues than Americans are. Some European governments have either taxed Nicad batteries so heavily they've become cost-prohibitive or they've flat-out regulated cadmium batteries so that users must buy NiMH-powered products--or plug in. That's why tool companies like Bosch, DeWalt, and Metabo are selling NiMH-powered tools in European markets even though they aren't marketing them in the United States.

Stateside, there's little pressure to change over to NiMH technology and more time to test it. Manufacturers like Bosch, DeWalt, and Porter-Cable say NiMH has potential, but their lab tests indicate that their users get the best overall tool performance, longest work hours, and longest cycle life from Nicad. (Please note that every toolmaker I spoke with said lab tests can't truly mimic jobsite rigors, so their conclusions require a bit of conjecture.)

Cycle life is defined as the number of times a battery can be charged and discharged before its run time falls below a pre-determined value, often 50 to 70 percent of its original capacity. Measuring cycle life in the field doesn't require special equipment: A pack is shot when it spends more time in the charger than on the tool.

Some toolmakers maintain that NiMH has less cycle life than Nicad does. Panasonic, the industry's only manufacturer that makes both batteries and tools, says that's not so. The company guarantees similar cycle-lives between its NiMH and Nicad packs. Depending on use, that amounts to 1,200 to 2,000 charge/discharge cycles. Plus, Panasonic says, NiMH batteries with longer run times have more total working hours.

Makita engineers tell a similar story. Their testing reveals that higher amp-hour (1.7 to 3.0) NiMH batteries provide slightly fewer charge/discharge cycles, but provide their tools with more total run time than equivalent Nicad packs do. That means the battery spends more time on the tool than in the charger and works longer. Panasonic and Makita agree, charger technology is very important for all power packs, but especially for NiMH cells.

A few years ago, the companies involved in the voltage race tried to get more cells in Nicad battery packs to power bigger tools. Now there's a technology race to master emerging battery chemistry. Bosch, DeWalt, Milwaukee, and Porter-Cable are improving performance on their Nicad platforms but are continuing to test NiMH technology. Panasonic (which still makes Nicad-powered tools), Makita, and Milwaukee are moving forward with the newer platform. According to several toolmakers, there's still plenty of mileage left in Nicad chemistry and amp-hours are said to be going up in the next 18 months or so. However, those toolmakers also say NiMH is the long-range future of an increasingly cordless world.

More Power?

Kits. Despite cordless tools' efficiencies, batteries can get expensive, even redundant, if you have enough tools on the same platform. There's also such a thing as having enough chargers; like batteries, you only need so many.

To soften the financial blow of buying multiple cordless tools, manufacturers sell kits containing some combination of drill/hammerdrill, recip saw, and/or circ saw in the same box. Many include work lights, too. You get several tools that run off the same power supply, but you don't get three separate chargers, three separate tool cases, and six batteries.

The high-drain tools in these kits need bigger batteries to function usefully. When buying kits, however, some users complain that if they buy into one of these high-volt platforms, they're stuck with tools that are just too heavy and they need to get lighter tools to work comfortably. That's the trade-off for eliminating costly redunacies.

DeWalt, for instance, knows a 24-volt driver is a brute and doesn't even bother with a clutch. In other words, they're fully aware that a tool this powerful or large will not be your go-to for setting cabinets or driving drywall screws. However, they do know that it -- and all the other 24-volters out there -- are game for drilling holes in sill plates or though 6-by materials where smaller tools would bog down in a hurry.

Purchasing cordless tools in kits or customizing your cordless fleet with multiple-voltage tools comes down to preference and pocketbook. Understanding battery specs can help you match tools to your jobs and eliminate guesswork.

Amp-hours. Since amp-hours measure run time, you might say they measure the size of the gas tank, not the motor's power. A 3-amp-hour battery works longer on a single charge than a 1.7-amp-hour battery, toolmakers say. So, if you spend long periods of time away from a charger or you just like the idea of a long-lasting battery, go for high amp-hours in either Nicad or NiMH chemistry. At 3 amp-hours, NiMH batteries offer the highest capacity (4-amp-hour models are expected soon). Nicad batteries currently max out around 2.6 amp-hours, but expect increases soon.

Trades in the field often tell toolmakers they want cordless tools with more run time. Again, that's a trade-off. Higher amp-hour batteries -- which supply more run time -- have shorter cycle lives. They heat up more than lower amp-hour batteries do, which reduces the number of times they can be charged. That's equally true for Nicad and NiMH batteries.

Power and run time. Power is a nebulous term in the tool world -- especially in cordless tools -- because you have to measure both the battery and the motor efficiencies. Since motor efficiency ratings aren't published, here's another good rule of thumb: Run time (expressed in watt hours) = volts x amp-hours. Keep in mind that this doesn't have anything to do with cycle life.

Yes, tool power has a lot to do with battery cells. A larger pack provides more stored energy than a smaller pack. But power is also derived from a tool's motor, gearing, and mechanical efficiencies beyond the battery. So, you can't judge a book by its cover, and you can't necessarily judge a tool's performance by its battery alone. But you have to start somewhere, and the battery is the only place you'll find enough information to start filling in the blanks.

Manufacturers like Bosch, DeWalt, and Makita have cranked up their voltage platforms to 24-volts and they supply seriously high-drain tools. Toolmakers have discovered that users buy more 24-volt specialty tools like rotary hammers and circ saws separately, than in kits. Combo kits are hot items in the 18-volt world, where a drill/driver isn't too heavy and the saws get the job done quickly. Milwaukee and Porter-Cable have found comfortable ceilings below 24 volts. Milwaukee platforms many of its high-draw tools on 18-volt batteries with 2.4 amp-hours, while Porter-Cable focuses on 19.2 volts with 2 amp-hour/batteries.

Twelve- and 14.4-volt platforms are still the most popular for drill/drivers, which are far and away the best-selling cordless tools sold. However, there's been major growth in 18-volt platforms like those offered by Bosch, DeWalt, Milwaukee, and Porter-Cable. Metabo has some of its higher-powered drills on a 15.6-volt platform, which provides the best combination of weight and power, the company says. Panasonic uses the same platform for many of its drills and saws because its higher-capacity NiMH cells produce the same torque, performance, and run time as 18-volt Nicad cells, but reduce tool size and weight.

Chemistry cost. Now that NiMH is out in tool lines from Makita and Panasonic, price may sway purchasing decisions. A NiMH battery pack generally costs a bit more for a toolmaker to buy than a Nicad pack, so you'll pay more for a NiMH battery. However, I found that cost difference wasn't much when I scoped out 12-volt drills with 3/8-inch chucks on the Web. The six tools I checked were within $35 of each other and the NiMH units weren't the most expensive.

Re-Charge

While NiMH vies for widespread use in the cordless tool market, the concept people at the battery manufacturers have their eyes set five years down the road on lithium ion battery chemistry. It's lighter than NiMH, lasts longer and takes up less space, but its performance characteristics need work to make them effective for power tools. Makita and Panasonic say they've mastered NiMH technology and have built a better cordless mousetrap with environmentally friendly batteries. Other's say Nicad's longer cycle life and better performance make it the superior technology.

A business element influences these positions. It's expensive for a company to re-engineer its tools. Makita and Panasonic have gone first and it looks like the rest of the industry is waiting to follow. But, while you're in your tool store trying to make a choice, remember this: A tool's feel, balance, weight, and features are still vital.