An o ring to fit the gap between the body and cap works with a longer battery, in case that helps.Unfortunately I found the 50mm batteries are just a tad too long for my provari minis creating an issue with completely screwing down the extension endcaps. The AW 18490 was 49mm. I bought nitecore 18490 button top that said they are 49.4mmm but they are 50mm, maybe my bottom springs are too stiff, others seem to be able to use the 50mm batteries.