Many newer e-cigs specify that their batteries must be rated for at least 20A discharge and they mean it. If you put old laptop cells and such it them (or flashlight batteries), there is a real risk of it failing "dramatically". Given how many people do that, I'm actually impressed and surprised that it's only 66.
Of course, I notice the FDA lumped everything from mild redness due to an overheat and something that might be describable as an explosion into the same category to fluff it up to 66.
So, use only batteries rated for 20A discharge or greater. Since a few "cloud chaser" devices need even more, be sure to read the instructions and use the appropriate rated batteries. Also make sure your PV's battery case is SIDE vented or has a magnetic battery door so it can't rocket itself into your mouth.
DO NOT use old LiIon batteries, use lmr batteries. The formulation is intrinsically safer.