DIAGNOSIS The blade is binding or the motor is straining. The primary cause is a dull or incorrect blade, or cutting material too thick for the saw's capacity.
FIX Stop the cut. Unplug the battery. Inspect the blade. Look for dull, chipped, or missing carbide teeth. Replace with a sharp, thin-kerf circular saw blade rated for your material. Ensure the blade is installed with teeth pointing forward.
IF THAT DIDN'T WORK The gear case may have insufficient grease or a damaged pinion gear. This requires opening the gear housing to inspect. Worn gears will need replacement.
HEADS UP This saw is for sheet goods and dimensional lumber. Do not try to cut wet pressure-treated lumber or concrete board. It will destroy the blade and strain the motor.