I've rotated 8 18650's forever and they all still perform well. Rotation slows down the number of recharge cycles each gets and makes them all last longer. Use the same two batteries over and over and they die much faster.
I wonder how long my iStick is going to last. Its wired in 18650 gets plugged in once or twice a day for short periods to get topped off. When the battery dies, the device gets tossed. That's a negative, IMO. You have to practically destroy the device to solder in a new one.
The good part of that is that it's a fairly cheap throwaway mod that vapes really well and fits in a pocket.
Actually, Taking an iStick apart is Relatively Simple. It just has to be done in the Correct Order.
1 - Remove the Two Taped on Plexiglass Strips around the Buttons.
2 - Turn the Unit over and the Buttons will Fall Out.
3 - Remove the Two Screws from the Top Cover.
4 - Remove the Two Screws from the Bottom Cover and the Bottom Cover.
5 - Push the Board and the Battery out the Top of the iStick Body.
Done.
Just don't make the Mistake I made. And start Poking things with a Dental Pick. Because since the Board is Hard-Wired to the Battery. The Board is "Live". And poking it with a Metal Dental Pick can release the Magic Smoke in the Board.