Battery life is about matching the device to the customer's habits. A heavy vaper needs a larger battery; a light user can get away with less. Don't push the biggest battery on everyone—that's a disservice. Look at the device's capacity and compare it to the puff count. If a device claims a high puff count but the battery drains first, that's a problem. The VERTEX-25K and VERTEX-15K are designed to balance battery and e-liquid, but verify for yourself. A quick test: charge one fully, use it for a day, and see where you end up.