Smart batteries and chargers for cordless tools

Batteries comprise about 50 percent of the total cost of a cordless tool system, and upgrading to a new technology can be costly. “Smart” batteries and chargers can help

Christian Corrigan -- Industrial Distribution, 4/1/2007 6:00:00 AM

As the fastest growing segment of the power tool market, cordless tools have grown at a rate that far outpaces other tools—including pneumatic and corded electric tools—over the last 15 years. A $2.7 billion worldwide market, cordless tools are now the biggest segment of the total power tool market.

There are several reasons for this, not the least of which is user convenience. In addition to far greater mobility, cordless tools provide many lesser known benefits. A recent report by the National Council on Compensation Insurance Inc. cited the increased use of cordless tools as one of the top reasons for the significant decline of workers compensation claims in recent years.

Reduced workplace noise is another important ergonomic benefit. Without built-in exhaust systems, cordless tools are much quieter than their pneumatic counterparts, in some cases as much as 20 times quieter. Cordless tools can also provide cost savings to industrial and construction users by eliminating the need for compressors, electrical cords and additional tool maintenance.

But perhaps the biggest reason for the surge of cordless tools is improved technology. Today's cordless tools are stronger and more durable than ever before, providing more power and significantly longer run times. While better tool housings, more robust internal mechanisms and other factors have contributed to this trend, new battery technology may be most responsible for the exponential increase in cordless tool use.

From lead-acid to lithium-ion

The first big development in battery technology occurred in the early 1970s with the commercialization of nickel-cadmium. Previously, the majority of batteries were lead-acid, which was heavy and didn't lend itself well to portable tools. With the commercial acceptance of nickel-cadmium, batteries were smaller, more energy-dense and less expensive than their predecessors.

However, nickel-cadmium batteries created environmental concerns when it became evident that cadmium was difficult to dispose of safely. To solve these problems, manufacturers developed an alternative battery chemistry known as nickel-metal hydride. Although nickel-metal hydride batteries were easier to dispose, they were significantly more expensive. The cost of upgrading to the new battery chemistry was too prohibitive and mainstream adoption was never fully realized.

Then, in 1991, battery technology took a quantum leap with the commercialization of lithium-ion batteries. Comprised of the energy-dense element lithium, lithium-ion batteries delivered an exceptional amount of power in a much lighter package. In these early days, however, even lithium-ion batteries had drawbacks. The new technology quickly powered the development of electronic products such as laptops and cell phones, but batteries powered by lithium were too volatile for high-current draw applications.

In recent years, tool manufacturers have begun using lithium-ion batteries to power cordless tools. With the introduction of new chemistries such as lithium-cobalt, lithium-manganese and others, batteries are now capable of handling applications with higher current draws, making it more feasible to use cordless tools in demanding industrial and construction workplaces.

Batteries today

Today, lithium-ion batteries represent a vast improvement in technology, potentially delivering much greater productivity than other chemistries. Lithium-ion batteries last longer and are far less susceptible to voltage depression, common in nickel-cadmium batteries. Known as “memory effect,” voltage depression occurs when a battery exhibits a decreasing charge capacity over time, caused by placing a battery on a charger before its charge has been completely drained or taking it off the charger before it is finished charging. The battery then “remembers” its charge level and recalibrates itself, decreasing charge capacity.

Not surprisingly, lithium-ion batteries also outperform other chemistries in power consistency. The batteries maintain the same charge for the entire cycle while nickel-cadmium batteries tend to slowly lose their charge and power as they are used.

Nickel-cadmium batteries, however, still hold one powerful advantage over lithium-ion models: they cost an average of 50 percent less than lithium-ion batteries. In fact, despite being on the market for nearly three years, lithium-ion batteries comprise only 5 percent of the overall battery market, while nickel-cadmium batteries make up more than 60 percent. Customers often find it difficult to make the switch because upgrading means investing in an entirely new platform —buying new batteries, new chargers, and in some cases, even new tools.

Trends in battery technology

Some manufacturers have begun fighting this issue by developing “smarter” batteries and chargers. Some of the most advanced power systems on the market now feature batteries with integrated microprocessors that sense battery condition and communicate to the charger. The charger “reads” the battery and optimizes its charge based on the information it receives, improving battery performance and longevity. Additionally, the charger automatically detects battery voltage and chemistry, choosing the correct charge algorithm. This enables operators to use the same charger for multiple voltages and chemistries.

Some manufacturers now produce chargers with “renew” capabilities. These chargers force the battery to completely discharge and recharge every time, giving the battery a deep cycle refresh and restoring it to like-new condition. The charger also calibrates battery electronics. For nickel-cadmium batteries, this feature eliminates memory effect, significantly extending usable battery life and decreasing the number of replacement batteries over the life of the tool.

In addition to better electronics, manufacturers have improved the tool-battery interface. The stem pack is the traditional tool-battery interface and has been in use since the inception of cordless tools. It allows users to connect the battery to the tool by fitting a cell into the handle, making the battery more compact and more ergonomic. However, with a stem pack design, battery weight rests on the battery clips, causing it to eventually fall out with normal wear and tear. Slide packs address this problem by implementing slides on the bottom of the tool housing to hold the battery.

The disadvantages of this design include larger batteries and dead space in the tool handle. In addition, although the battery securely locks into place, battery weight is held on the bottom-most portion of the housing, causing them to break easily when dropped. The twist pack utilizes the best of both interfaces by fitting into the handle and twisting until locked into place. This twist-lock design spreads the weight of the battery evenly and takes advantage of dead space in the handle.

Power in the future

With more money invested in battery development than any other electronic technology, batteries will not stop at lithium. Many improvements are just on the horizon. Some manufacturers have already begun producing batteries that can be programmed to be backwards compatible. Market pressure may eventually force manufacturers to transfer charger technologies into their batteries to allow users to continue to use the same charger, even as new technologies reach the market.

Manufacturers will also continue to develop new chemistries that are more durable and efficient. New technology will explore ways that cordless tools can pull more energy out of their batteries, faster. Battery capacity will continue to increase, expanding amp-hours while decreasing size.

New technology is also likely to significantly decrease charge time —possibly even eliminating the need for chargers altogether—providing an alternate means of replenishing battery energy. Laptops, cell phones and other low-current draw products already utilize shapeable batteries. The standard power tool battery today is cylindrical, but that is likely to change as battery chemistry becomes more advanced. With the ability to configure batteries, new product designs might place them inside the tool handle or hammer case, eliminating the need for a clip-on battery at the base of the tool.

However, the biggest hurdle for new technology to overcome is still cost, as batteries comprise about 50 percent of the total cost of a cordless tool system. Until manufacturers find a way to make it affordable for customers to upgrade to new technology, the market will continue to adopt slowly.