i have been using the sony 4.2 v us18650s that came with my v3 vamo(fast tech) and if i let it sit a couple of days after charging in the case while i use the other bat up i get low v after a little bit of use i pull it out and reinsert it and it works ,all the while it's still reading say 4.1 v what's up with that? just started after 3-4 weeks,otherwise no problems