They are not the same. 18490's are a shade shorter. The ProVari was designed specifically for the 18490's. The batteries are required to be button tops as that is part of ProVape's reverse battery protection. If you use 18500's you might over compress the battery spring and cause undo stress on the control board. I was told by the B&M owner NOT to use any 18500's, but some folks who have been here much longer and had their ProVari's longer than I have will be able to provide better guidance.