Battery-powered tools are able to handle tougher jobs than they ever could before. Battery life is longer while tool weights have become less.
Milwaukee Electric Tool Battery-powered tools are able to handle tougher jobs than they ever could before. Battery life is longer while tool weights have become less.

You probably own all the corded tools you need to perform your company's work. So why would you discard that investment to buy into the latest cordless trend being promoted by tool manufacturers? As it turns out, there are many good reasons to go cordless, the primary reason being the constant improvements in battery technology and the growing number of tools using battery power, especially tools that need more power (watts).

Not long ago it was believed these tools would always be plugged into outlets.

Battery tool technology can be confusing because there are many choices. It starts with the three types of batteries currently powering tools today: Nickel cadmium (NiCad), nickel metal hydride (NiMH), and lithium ion (Li-ion). The new kid on the block is Li-ion but that doesn't mean that NiCad and NiMH will be phased out any time soon, they won't. Each battery has its advantages and disadvantages.

Benefits Of Cordless Technology

Developments in battery-operated tools intended for jobsite applications are advancing at a rapid pace. Tools are becoming smaller; they weigh less, and in some cases can out perform their corded cousins. Batteries are increasing in voltage and lasting longer too. In remote places where power isn't available, you don't need to set up a generator, you just pick up a tool and begin your work. And in areas that have power available there is no setup needed for laying out extension cords before work begins—expensive cords with short life spans that are susceptible to OSHA fines.

The Basics

The power required to operate a tool is measured in watts, W (watts = volts x amps). If you think of electricity as a fluid, voltage (V) is equivalent to the pressure while current (measured in amps, A) is equivalent to the speed at which the fluid moves through the pipe. Power is therefore equivalent to the flowrate—basically the amount of electrons being delivered. You can increase power by increasing the volts, the amps, or both. So, for example, a 36-V tool can accomplish a harder task than an 18-V tool, such as powering a 1-inch rotary hammer.

The voltage of two batteries may be different, but what they can deliver depends on their Watt-hour rating, commonly referred to as runtime or more scientifically as “energy.” You can estimate runtime by multiplying the battery's voltage times its amp-hour rating. Manufacturers often show voltage and amp-hours in big letters on the sides of their batteries. Amp-hours can be equated to the size of the gas tank in your car—the larger the tank the farther you can travel.

A battery with a higher Watt-hour rating can draw more amperage for a longer period of time. For example, if a 36-V battery has 3 amp-hours, it has 108 Watt-hours. It will supply the needs of a given tool longer than an 18-V battery with 3 amp-hours with 54 Watt-hours.

Batteries are made up of individual cells, basically independent batteries, which are wired together in series to make up the operating voltage of the battery. Li-ion is different from NiCad or NiMH in that it allows batteries also to be wired in parallel to help increase the battery pack's amp-hours for more runtime.

Besides your typical jobsite abuse, the enemy of all batteries is heat. Edwin Bender, product manager for cordless products for Bosch, Mount Prospect, Ill., says that “heat, over time, is what kills batteries.” For this reason manufacturers include heat sensors, electronics, and tool designs that manage heat build-up. Heat is a concern while batteries are being charged too. So chargers also include systems to manage heat in batteries during their charging cycle.

Battery-Operated Tool Features

Brad Wheeler, product marketing manager for Makita USA, LaMirada, Calif., says that tool ergonomics are very important. The tool must feel comfortable in your hands and there should be good balance between the tool and the battery. Because there are more cells in nickel-based batteries, space is an issue. To address this, some cells are mounted on top of the battery, sliding into the handle of the tool. Handles are more restricted in their design as a result and this influences how tools feel in your hand. With Li-ion batteries, cells can easily be fit in the body of the battery, making it possible for manufacturers to have slide-on connections to the tool. This provides manufacturers with the opportunity to design tool handles to fit your hand more comfortably. Wheeler says their Li-ion battery-powered tools often have redesigned motors and tool assemblies that make them smaller and better balanced.

Tool companies provide tools with low voltages that have plenty of power. Shown here is a 10.8-V drill/driver with a Li-ion battery, making it both light and small enough to fit in your pocket.
Bosch Tool companies provide tools with low voltages that have plenty of power. Shown here is a 10.8-V drill/driver with a Li-ion battery, making it both light and small enough to fit in your pocket.

The trend with battery-powered tools is to make them both smaller and lighter. And many manufacturers also are developing tools with both higher and lower voltage platforms. Li-ion batteries especially provide opportunity here. Bender says the user can choose two options with their 36-V Litheon platform—a slim pack that weighs less than a 14.4-V nickel-based battery and runs 15% longer than an 18-V nickel-based battery or a standard pack that weighs only 3 ounces more than an 18-V NiCad battery, ideal for applications that require longer runtimes or higher power. Higher-voltage platforms are ideal for SDS rotary hammers and chippers, circular saws, reciprocating saws, and impact wrenches. Circular saws especially have come of age in this category. On the low voltage side—10.8 V or less—tools include drill/drivers, impact drivers, and wrenches. These powerful tools are small, ideal for work in tight spaces, and you can easily carry them in your pants pocket or tool pouch.

Mike Sheriff, professional power tool manager for Ridgid power tools, Anderson, S.C., says that another trend is to sell tools without batteries, making it economical to own several tools powered by one battery. So manufacturers offer several tools on the same voltage platform—especially attractive for the more expensive Li-ion batteries.

Batteries And Chargers

All three batteries—NiCad, NiMH, and Li-ion—will remain on the market for the foreseeable future and manufacturers continue to design tools for each of them. Keep in mind that an 18-V battery with a 3 amp-hour rating delivers the same amount of power to the tool regardless of whether it is NiCad, NiMH, or Li-ion. The differences are size, weight, and number of recharge cycles.

Batteries developed by one manufacturer aren't the same as batteries developed by another because of the differences in chemistry they use. They also have different views about the best way to charge them, protect them, and design tools around them. But there are some general commonalities.

NiCad batteries. They were the first ones used to power tools and have a 20-year history now. A major advantage is that they cost less than either NiMH or Li-ion batteries. A major disadvantage is that they are made with cadmium, an environmentally dangerous element. Manufacturers encourage users to return them for recycling when they are spent but only about 10% of them ever get turned back in.

The individual cells in a NiCad battery are 1.2 V so 12 cells are needed to make up a battery with 14.4 V. Doug Bock, group sales manager for the power tool division at Panasonic, Secaucus, N.J., says that NiCad battery technology tops out at 2 1/2 amp-hours. As the voltage goes up, so does the weight so there's a point where tools are too heavy to be ergonomically friendly. For this reason, NiCad batteries tend to power tools in the mid-voltage ranges.

NiMH batteries. Panasonic and Makita were the first manufacturers to start using NiMH batteries. It was partially an industry response to provide a more environmentally friendly battery but they have other advantages. Bock says they can store 45% more energy than NiCad batteries in the same sized cell with up to 3 1/2 amp-hour ratings. David Schimmel, director of power tools marketing for Hilti North America, Tulsa, Okla., adds that the efficiency of these batteries increases as their amp-hour ratings increase. They can operate at lower temperatures than either NiCad or Li-ion batteries also. And Christine Potter, a product manager for Dewalt, Towson, Md., says that technology improvements in the near future will increase their life cycle.

Li-ion batteries. There are more than 100 different chemistries used for making Li-ion batteries. They power your cell phones and your laptops. But those batteries are very different than the ones that power your tools. These are designed for high-amperage output and therefore have both electronic and mechanical systems built into them to manage heat, being very different than the batteries in recent news reports that have caused laptops to burn up. Milwaukee Electric Tool was the first to introduce Li-ion battery power tools in early 2005 and although they are new they also have more than 10 years of laboratory research behind them. Their big advantage is weight—being as much as 30% less than NiCad.

High-voltage platform circular saws are winning converts because of their long run times.
DeWalt High-voltage platform circular saws are winning converts because of their long run times.

One reason that Li-ion batteries are lighter than NiCad or NiMH is that an individual Li-ion cell produces 3.6 V (versus 1.2 V for NiCad). So only four cells are needed to make a 14.4-V battery compared to 12 cells for NiCad.

Bender says that Li-ion batteries have longer run times and offer manufacturers choices regarding power and weight. Li-ion batteries can provide more power at the same weight as NiCad or NiMH or the same power at a lighter weight.

A problem for all Li-ion batteries is that when they are fully discharged they can't be recharged. So all manufacturers electronically monitor their batteries to prevent them from completely discharging. These monitoring devices are located either in the battery or the tool depending on the manufacturer. For example, Terry Tuerk, product manager for Metabo, Westchester, Pa., says when its Li-ion batteries reach 2.2-V, the battery shuts down.

Potter says that unfortunately, there is no standard methodology for testing cycle life in the power tool industry so it's hard to compare how one battery performs compared to another. She adds that Li-ion batteries at light discharges can be recharged many more times than NiCad or NiMH. At higher discharge levels, though, many Li-ion formulations won't recharge as many times.

Chargers. For comparison purposes, it would be nice if all chargers were alike, but there are big differences here as well, starting with charging time. Some manufacturers believe it's best for batteries to charge over a longer period of time while others offer fast chargers that can cut the time in half. Depending on the manufacturer, they are sold to serve only one type of battery or a wide range of batteries.

Schimmel says NiCad and NiMH batteries have another problem. “The cells in nickel-based batteries discharge at different rates. Recharging stops when the first cell is fully charged, leaving the other cells with less charge.” This also means that when one cell discharges before the other cells, the battery must be recharged. This condition is referred to as “memory effect.” Schimmel says that some manufacturers solve the problem by selling chargers with a “refresh cycle.” They deplete all the cells of power before charging begins, making it possible to recharge all the cells to the same level. There is no need to do this for Li-ion batteries.

Chargers are becoming more sophisticated. They have electronics built into them that communicate with batteries to monitor temperature and charging rates. And some have built in fans that circulate air through vents in batteries to reduce their core temperature while charging—especially Li-ion battery chargers.

Charging time can be as little as 15 minutes for low-voltage batteries and as much as one hour for higher-voltage batteries. Li-ion batteries take 30% less time to recharge. Manufacturers make the decisions that determine charge time.

Expected Life

Manufacturers are hesitant to talk about what the expected life of a battery should be, though all of them offer warranty periods and most also offer free extended service packages—activated by registering the tool. They aren't worried about their tools, it's how they are used and how batteries are cared for that determines how long they will last.

Another factor has to do with the chemistry of batteries, which varies among manufacturers. Battery life is usually reported as the number of discharge and recharge cycles you can expect rather than in years of life. So for instance, your tool supplier may tell you that you can get 500 cycles from the NiCad battery in your drill/driver. As a general rule, Li-ion batteries have higher cycle lives than NiCad or NiMH, and higher-voltage platforms have a shorter life span than low-voltage platforms.

Cycle life can be as little as 400 recharges and as many as 2000 depending on the battery chemistry, how a tool is used, and the amount of heat the battery is subjected to.

Voltage Platforms

Cordless power tools are available up to 36 V. They are capable of performing tough jobs for extended periods of time.
Bosch Cordless power tools are available up to 36 V. They are capable of performing tough jobs for extended periods of time.

Schimmel says there are two ways companies rate voltage for batteries: charge and discharge volts. Most companies rate their platforms by discharge volts. You can tell which is being reported by dividing the rated voltage by 3.6 for Li-ion and 1.2 for nickel-based batteries. If the result is an even number (of cells), then the rated voltage is discharge volts.

There are many voltage platforms currently on the market for nickel-based and Li-ion batteries, rated both as discharge and charge volts. Platforms for nickel-based batteries are 3.6, 7.2, 9.6, 12, 14.4, 15.6, 18, 24, and 36 V; for Li-ion, batteries are rated at 3.6, 7.2, 10.8, 14.4, 18, 21.6, 24, 28, and 36 V. The platform that is currently the most popular, with the largest number of tools available, is 18 V. Bigger isn't always better though; you should choose the platform that best fits your application.

The Value Of Cordless

Learning about and keeping up with battery technology can be, in some ways, more important than learning about the tools themselves. Portable electric tools have been on the scene for a long time and although their development continues, it's battery technology that's changing the most rapidly right now. Tools with higher voltage battery platforms are the current “hot” spot. It's amazing how well and how long these tools can perform. The market is growing fast and we are learning about their true value as we go.

Download a PDF chart of cordless tools currently on the market.