Comparison of Cordless Drill Run Times

Voltage

• Voltage is, in essence, a measure of the force that moves usable electrical energy around. The amount of usable electrical energy delivered to the point of use -- the drill’s motor -- is directly proportionate to the voltage: the higher the voltage, the more powerful the drill should be.

Torque

• Torque is a measurement of the strength that the drill’s motor puts out as rotational force. Speed of revolution is different from torque. The drill’s speed is measured in revolutions per minute, or rpm, while torque is measured in foot-pounds or inch-pounds. Increased torque does not necessarily result in an increased rpm. However, a drill with higher torque can drill without stalling through tougher material -- or drive fasteners into a more resistant substrate -- at a greater speed than a less torqued competitor.

The Voltage-Torque Equation

• A drill with a lot of torque spins faster, and continues to spin when drilling through very resistant materials, for longer than a motor with less torque. Run times depend upon the relationship between voltage and torque: A heavier-voltage battery may be drained more quickly by a massively torqued motor than a lower-voltage battery powering a smaller motor.

Available Voltages and Torques

• The most common voltages for cordless drills are 9.6-, 14.4-, 18- and 19.2-volt. Some up-market, professional-grade tools are available in 24-, 28- and 36-volt models. As noted, increasing the voltage does not necessarily result in an increased run time, but greater torque results in a much more robust drilling performance even over the same useful amount of time. While manufacturers brandish the voltage of their products loudly on their packaging, they seldom reference torque. That said, a high voltage typically indicates a high torque, also, and heavier chucks able to accommodate larger bits and drivers are another good indicator.

Application

• Strictly in terms of run time, a great deal of performance overlap is available on the shelf. A 9.6-volt drill with a low torque would be entirely adequate for a pilot drilling soft wood for several hours, while a 36-volt drill with a massive torque might have the same run time when used for driving concrete anchors. Application is an important consideration when planning a purchase.

Batteries

• As of January 2012, three main types of rechargeable batteries are used to power cordless drills. Nickel cadmium, or NiCad, was the first rechargeable battery that successfully balanced size-weight considerations with power delivery. Although this type can afford a long working life, it must be treated somewhat gently; full discharge-recharge usage cycles shorten their lives considerably. Nickel metal hydride batteries, or NiMH, are less sensitive to full discharge issues and do not have the environmentally dangerous element cadmium as a component. Their working life, however, is considerably less than the 1,000 charges their predecessors could take. Lithium ion, or Li-Ion, deliver a great deal of power for their size and are very resistant to damage in the recharging process. They are, however, comparatively expensive.