I'm looking to buy a provari v2 and want to use the 10 18650 batteries, with the extension cap can I use the 18650 battery that are like 65mm long, not the flat top?? I don't have the flat tops, I just have the longer (regular) 18650 batt. Just want to make sure the extension cap will fit my regular battery not only the flat top 18650. Please let me know so I can buy with certainty. Thanks