The Hercules HC91K1 is part of the Cordless Drill
test program at Consumer Reports. In our lab tests, Cordless Drill
models like the HC91K1 are rated on multiple criteria, such as those listed below.
Speed: How fast the drill can drill holes and drive screws
Power: Represents the amount of work produced by the drill from max RPM to stall. This is accomplished by increasing the applied torque on the dynamometer at a constant rate for a constant time period.
Run time: Reflects how much work the drill can perform per battery charge, as measured on a dynamometer.
Battery typeThe type of batteries provided with the drill. All are rechargeable. The more common type is denoted Li-Ion for Lithium-ion. Another common type is denoted NiCd, for its nickel-cadmium components. Lithium-ion batteries tend to deliver more power in a smaller size when compared to nickel-cadmium.
Battery recharge time
Battery recharge timeHow long it takes to completely recharge a battery after it has properly cooled down. Most of the fast chargers have a built-in temperature sensor that delays the charging cycle, when the battery is too hot from recent heavy use, to when the battery has cooled.
Speed rangesMany cordless drills have two separate speed ranges, or gear ratios; some newer models have three. The slower speed range peaks at about 400 revolutions per minute (rpm) and provides increased torque (twisting force) for driving large screws. A higher speed range that reaches about 1,500 rpm or more is well suited for rapid drilling. Lower-priced drills usually have a single speed range that tops out at approximately 600 to 800 rpm, compromising both driving and drilling performance.
Chuck capacityIndicates the largest size full-shank tool (twist drill bits on power drills) that a drill's chuck can hold. Common sizes include .375 inch (3/8 inch) typically for general usage, and .5 inch (1/2 inch) for drill intended for heavy duty jobs. Fixed 1/4 inch hex chucks only accepts 1/4 inch screw bits or special drill bits.
Maximum RPMTwo and three-speed cordless drills have a maximum speed of about 2000 revolutions per minute (rpm) or more and can easily handle rapid drilling. Many lower-priced, single-speed cordless drills can manage only about 600 to 800 rpm, compromising their performance.
Clutch settingsVirtually all cordless drills have settings that can limit maximum torque and so prevent the drill from driving a screw too far into soft wallboard, say, or mangling a screw's head or threads by continuing to turn after the screw is in. The more settings, the more precise the torque control.
Number of batteries included
Number of batteries includedA second battery lets you keep working while the first recharges, so that your work can continue. Most drills over $100 include two batteries.
Hammer modeAn additional selectable feature that pulses the chuck and drill bit back and forth to assist in drilling through masonry and similar hard materials.
LED work light
LED work lightA small light, located on the body of the drill, to help in low-light job conditions.
WarrantyThe length of the coverage, in years.