Guy's unless you know what you are doing and feel Confident in the Knowledge you have acquired to Stack batteries then don't do it. That you are Fanatical about How you use the ones for stacking and use them Only for stacking, you rotate them, you name them, you keep notes on which ones you placed on top/ bottom last At last use, you meter/test them every single time you use them, you maintain a set of notes on degradation, etc. etc.
I would Not Recommend anyone Stack batteries UNLESS they Know what they are doing.
Please Read TC1's Thread on Batteries Explained . He wrote it for Your safety, please read it.
Sounds like too much work, lol.
I'll just stick with my original plan and use the 18350's for "stealth mode".