You have been using lithium-ion (LI) batteries in your cellphones, digital cameras, and laptop computers for almost 10 years. And now, after 10 years of research and development, major tool manufacturers are introducing LI batteries for your power tools too—far different from the batteries that power your cellphone. Lithium-ion batteries deliver the high amperage needed to run rotary hammers, hammer drills, drill/drivers, and other tools common to construction sites. They are smaller, lighter, and store much more current then nickel cadmium (NiCad) batteries.
You might think there's been a constant stream of new battery technology, but that's not the case. NiCad batteries have been the industry workhorse for more than 10 years. The technology has been
improved from time to time, but although nickel metal hydride (NiMH) appeared a couple years ago, LI battery technology is in the first big breakthrough that will dominate the cordless tool market for the next 10 years. And even though tool manufacturers are just introducing LI battery powered tools, several years of research and development back them up.
Sticker shock might make you think twice about buying LI batteries because NiCad batteries are considerably cheaper. But LI batteries pack much more power and will increasingly power tools once considered only corded. When you think about it, your most expensive tool-related purchase is probably extension cords. A reasonable quality, 50-foot, 12-gauge power cord rated for construction site use can cost as much as $35. Jobsite conditions can quickly render them non-OSHA approved, so you frequently end up replacing it. And if your work is too far from a power source, generators become part of your tool kit. Including the labor to set it all up each day, the cost of LI technology is probably a bargain.
There are more than 100 lithium compounds being researched for use as batteries according to Christine Potter, group product manager for DeWALT Power Tools, Towson, Md., but only a few of them have the properties needed for high current output. DeWALT introduced nano-phosphate-lithium batteries; Milwaukee Electric Tools, Brookfield, Wis., sells lithium-manganese batteries; Metabo, West Chester, Pa., uses lithium-manganese-cobalt batteries. These compounds probably won't mean much to you—and each company markets its chemistry as the best—so for the purpose of this article, the focus will be on the generic properties of LI batteries.
Here are some of the characteristics shared by all LI batteries:
- For their size and weight they can store twice as much energy as NiCad batteries. Manufacturers refer to this as “power-to-weight ratio,” and they take advantage of this by providing either lighter batteries (compared with NiCad) or higher voltage batteries without a weight penalty.
- Though they operate best in the same temperature range as NiCad batteries—between 40º F and 170º F—heat is of particular concern because it reduces a battery's cycle life. Tools with high voltage output can potentially produce more heat too.
- Unlike NiCad batteries, LI batteries don't have “memory” problems, meaning that they can be charged at any time during their discharge cycle without reducing the battery's capacity.
- From fully charged to fully discharged, LI batteries maintain flat voltage, meaning that the power performance is very even. NiCad batteries go from good performance to low performance as they discharge.
- Because of charging systems, LI batteries charge much more quickly than NiCad.
- Individual LI cells have a 3.6-volt operating capacity. NiCad cells, by contrast, are 1.2 volts. So five LI cells in series make an 18-volt battery compared with 15 NiCad cells.
- Because the deep discharge of LI batteries can damage the pack's individual cells, every manufacturer includes electronics to prevent total discharge.
- LI batteries have a long shelf life and can be stored without use for one year or longer.
- They can be recharged up to 2000 times. NiCad, by contrast, typically takes many fewer recharges.
- LI can be recharged at any time during their discharge cycle without consequences.
- There are no heavy metals in LI batteries, so they are more environmentally friendly, but still should be recycled properly. Visit www.call2recycle.org for locations.
- LI cell geometry favors horizontal battery designs, so batteries often slide horizontally to connect with tools.
As you can see, LI batteries have a lot going for them. But there are challenges too, the most important being heat management, which also involves power management. This is where the tool companies have spent much of their R&D money. Their choice of battery chemistry, decisions about battery case designs, voltage platforms and amp-hours, the development of elaborate electronic surveillance, management of battery functions, the creation of new charging technology, and the introduction of tools to take the best advantage of the batteries capitalize on the benefits while managing the problems related to heat development in the batteries.