mAh (milliampere-hour) tells you how much energy a battery holds. For vapes, a higher mAh usually means longer use between charges, but how long it actually lasts depends on wattage, coil, and your puffing style. If you're stocking shelves, you need to match mAh to what your customers actually do. The Windbar Vape Battery Calculator at /tools/vape-battery-calculator does the math for you.