Many cordless tools do not always operate at their maximum voltage because they often feature variable-speed triggers that allow you to adjust the tool's power output. In this context, 18V represents the maximum output rather than the voltage delivered every time the trigger is pulled. Watts, on the other hand, measure the total power consumed while the tool is in use. This is why light bulbs are typically rated in watts; unlike power tools, bulbs usually operate at a constant energy output-a 40W bulb consumes 40 watts almost continuously.
Unlike voltage, watts measure power. So yes, a higher wattage means greater power. An 18V impact wrench used at a low speed setting remains an 18V tool, but its wattage fluctuates in real-time based on the rotational speed. Consequently, the higher the wattage a cordless tool draws at any given moment, the faster the battery drains. After all, a battery is a finite energy source, and higher wattage implies a greater rate of energy consumption. The same applies to corded tools: while the power supply may be virtually limitless, higher wattage results in higher electricity costs.
The distinction between watt-hours and watts is that a watt-hour represents one watt of power consumed over the course of an hour. A tool with a power rating of 1,000 watts consumes 1,000 watt-hours-or 1 kilowatt-hour (kWh)-when operated for one hour. Watt-hours are also a crucial factor when purchasing portable power stations, as the kWh rating indicates the total energy available before the unit runs out of power.
Higher wattage does not necessarily equate to better performance; it simply indicates that the tool is consuming more power, not how efficiently that power is utilized. For instance, older tools with brushed motors generate significant heat and friction, resulting in wasted power. Modern brushless tools often deliver superior performance at the same wattage.
Complicating matters further is the distinction between running watts and starting watts. Running watts refers to the power consumption during normal operation, whereas some tools require a surge of power to start-known as starting watts-which can be two or three times higher than the running wattage.
Understanding a tool's starting wattage is important because exceeding the power capacity of the battery, generator, or grid can trip a circuit breaker or trigger an automatic shutdown. This is also where voltage matters, as it indicates the tool's potential current flow-an 18V tool powered by an 18V battery will never deliver more than 18 volts.
So, what about amperage? What is the deal with them? Amperage measures electrical current and, alongside voltage and wattage, forms one of the three fundamental elements of electricity-since wattage is calculated by multiplying voltage by current. This means that to achieve higher power (wattage) at any given moment, one must increase either the voltage or the current. Consequently, a 12V tool requires higher current to deliver the same power output as an 18V tool. Amperage also defines battery capacity in terms of amp-hours (Ah), measuring the accumulation of current over time. Therefore, a 12 Ah battery in a 40V system has twice the capacity of a 6 Ah battery, as its amp-hour rating is double that of the latter.
