Used in Cell phones and computers for years, Lithium-ion batteries were never powerful enough to run power tools until recently. The technology has now been refined for this use. Besides the other benefits, they are much more eco-friendly than the Nickel-Cadmium batteries, but still should be recycled properly. They are lighter in weight so you get more power with less fatigue. They hold a charge throughout the work until they just can't turn on the tool. Remember the time when you were in the middle of driving a screw and the battery just wouldn't sink it flush? That won't happen with the Litheon batteries. They will finish the screw but will not start the next one when they are drained. They run better in extreme weather (hot or cold) for those who work outdoors or store your tools in a truck.