Stacking, charging, and using unprotected Li-Ion batteries requires some knowledge, care, and proper procedures. They are dangerous. Added to that is our application really operates at the limits or outside of the operating range of the batteries we use. Max discharge rate of most of these batteries ranges from .5 amps to 2.5 amps. A 2.2 ohm load at 7v is going to try to draw close to 3 amps. and we're putting them in metal tubes we hold up to our face.
There were some unfortunate incidents/accidents. There are liability concerns. So it's not recommended.