unprotected cells in series? What if:
2 volts on the "weak battery" 3.7 volts on the "strong battery" plenty of volts to vape with. Just might be ONE VAPE AWAY FROM BLAM.
Make sure the battery that is going to BLOW is in the end AWAY from your FACE.
A single battery MOD using unprotected batteries can be monitored for weak vapor, stops vaping, stop sucking.
A stacked battery mod might use one battery to forcibly blow the other up.
Would have vaped just fine the vape just prior to the accident.
Rocketman