Energetic Cordless Tools

Purchasing Power

By Josh Garskof

We live in the cordless age. We can call home from the Interstate, compute at 30-thousand feet, and get an electric shave wherever we please. Old-house work, too, has become more convenient with the growing array of battery-operated tools. They are the hottest selling tools for both professional and amateur woodworkers. 

If you're shopping for a substantial tool that carries its own power supply, you'll find the shelves stocked with products that cost between $100 and $500. You'll come across voltages ranging from 9.6 volts to 2.4 volts. Plus you'll see highly charged marketing that touts mysterious features like fuzzy-logic and soft-pulse technology. Here's how to get the best product for your hard-earned money and for your own brand of work. 

On Volts and BatteriesThe most noticeable advance in cordless tools is ever-increasing voltage, which means more power. The first cordless drills, popular in the early 1980s, ran on just 6 to 7.2 volts, not enough for more than finish carpentry. Until a few years ago, 9.6 volts was the industry standard. Now most companies offer 12- and 14.4-volt products and many sell 18- and 24-volt tools. 

What does all this mean? To put it simply, volts measure electrical force. Think of circuitry as a pipe and electricity as water moving through it: voltage is akin to water pressure. Bigger, stronger batteries are needed to power reciprocating saws and hammer drills, but not other tools-such as light-duty saws, finish sanders, or the most popular cordless tool of all: the 3/8 drill/driver. 

Ask yourself how much power you really need because a supercharged battery will drain your wallet. More importantly, holding all that power in your hands can be tiring. Most 9.6 volt drills weigh under 4 pounds. Each jump in battery pack size from there can add 1/3 to 1/2 pound. Since the components of a battery have a given weight, the only way to lighten a tool besides reducing voltage is to use a lighter motor, which reduces power, or thinner plastic housing, which makes the tool fragile. Ergonomic design (such as T-handled drills) helps balance the tool, but doesn't lighten the load. Heavy drills tend to rotate in your hand, making it tough to drill a straight hole. Will you want the added mass that comes with extra power when you're working long hours or operating the tool overhead?

When you're operating high in the air or in a building without power supply, just how long a battery will last between charges may be more important than how much brute strength it has. Battery capacity is measured in ampere-hours-the quantity of electricity supplied over time. If voltage is the water pressure in a pipe, amperes are the volume of water passing through the pipe at one point. Amp-hours are a way of expressing this flow over time (amperes x hours). 

Cordless tool batteries generally run from 1 to 2 amp-hours. You can't translate this into specific amount of time because every task drains a tool differently, but the higher this number is, the more stamina you can expect. 

Best in Performance
So far, we've looked at what the battery can do. But the battery doesn't spin the 1' auger bit or carbide-tipped saw blade, the motor does. High-voltage batteries provide the potential for more power, but the tool has to take advantage of it. The strength of the motor, the gearing ratio, and the resistance of the wiring and switches, among other things, affect the tool's output. (Resistance limits the flow of electricity, like the diameter of a water pipe.) A beefy battery with a small motor, for example, may accomplish less than a powerful motor that requires fewer volts. 

So how do you determine a tool's power and run time? In addition to the battery's specs, check out the performance data of the whole package. The best measurement of brute force for drills is the torque (turning force) of the bit; for circular saws, compare revolutions-per-minute; for reciprocating saws, look at strokes-per-minute. To determine capacity, investigate the runtime of the tool on a single charge. The numbers that manufacturers report can be hard to compare because they use different tests. Make sure testing was done while the tools were doing similar tasks. 

Taking Charge
What really sets apart the best cordless products may not be the tool at all, but the charger. Battery packs will last anywhere from 500 to 3,000 charge/discharge cycles-largely depending on the quality of the charger. Recharging can take from 15 hours to 15 minutes. The fastest chargers are not only better for your patience, they're better for the battery. 

Chargers apply power to the battery where this electrical energy is stored as chemical energy. When the battery pack is fully charged, excess charge is turned into heat inside the battery. Heat is the most damaging force to affect batteries, and the amount of overcharge put on a battery influences how long it will last. 

Standard (or trickle) chargers are the slowest and cheapest. They're used in low-priced tools with fixed batteries, which are stored on their chargers. At their low charging rates, excess electricity during overcharge is dissipated as heat at non-damaging levels. 

Quick chargers recharge in three to five hours. These higher-quality battery cells are designed to handle the increased overcharge rate. Again, excess charge is dissipated as heat, but leaving the battery in the charger for a long time after it's full will shorten its life. 

Fast chargers are the best option for professional-quality power tools. They recharge the battery in one hour or less. At these high charge rates, overcharge would damage or even explode the battery pack. So, as the battery nears full charge, the units turn off, or switch to a safer trickle charge to top off the battery. 

What differentiates fast chargers is the way they determine when the battery nears maximum charge. Budget chargers measure the total electricity applied to the battery or time the charging process. Slightly better chargers read the voltage or temperature of the battery pack. Premium chargers monitor the battery with a number of these techniques-most importantly temperature and voltage sensing-and process the information with a computer chip. 

By watching all the battery's vital signs, the best chargers can accurately read when the battery is almost full, can slow down the charging process if the battery gets hot, and can eliminate certain other damaging forces. Whatever their proprietary name, these intelligent chargers completely control the charging process for the fastest and least damaging charge. The results are batteries that last for more than 1,000 cycles. If your tool comes with a choice of batteries, choose the higher cost of a high-capacity pack, which contains better cells. 

Professionals and homeowners alike have an amazing appetite for everything cordless. Manufacturers will continue to whet this taste with new cordless tools that have more power and capacity, and are more environmentally friendly. It'll take real breakthroughs in storing power to make possible the Holy Grail of battery-powered tools-long-ranging electric cars.

Thanks for technical assistance to Dave DeVries, Energizer Power Systems; Leslie Banduch and Dave Keller, Porter-Cable; Rich Mathews, DeWalt; and David Noggle, Skil-Bosch. 

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