Final answer:
Among the tools listed, a rotary saw often comes in small battery-powered units, making it a versatile and portable small electric tool.
Step-by-step explanation:
The question relates to identifying a small battery-powered tool, and among the options provided (hacksaw, chain saw, rotary saw, and circular saw), typically, a rotary saw is the one that comes in small battery-powered units. A rotary saw, also known as a rotary tool, can be a very versatile and small electric tool that operates on battery power, making it highly portable and convenient for various tasks.
Reciprocating motion in tools involves the conversion of the motor's rotational motion into linear motion. This is not directly related to the small battery-powered aspect but rather explains the operational mechanism of another type of saw known as a reciprocating saw. Unlike a reciprocating saw, a battery-powered rotary saw relies on a spinning motion to cut, grind, or sand different materials.