When evaluating portable fans, prioritize Battery Capacity (mAh) and Motor Type. Look for Brushless DC (BLDC) motors, as they offer higher energy efficiency, lower noise levels (typically <30dB), and a longer lifespan compared to brushed motors. For battery-operated models, ensure the use of rechargeable Lithium-ion batteries with safety protections against overcharging and short-circuiting. Additionally, verify the Airflow Velocity (m/s) and the number of speed settings to ensure the product meets diverse user needs.