Both Wiens and MG said a supply-chain attack in which a remote-triggered explosive was surreptitiously placed into the pagers before they were distributed is more likely. There is precedent for this: in 1996, Israel put a bomb inside of a cell phone and used it to kill Yahya Ayyash, who was then a bomb maker for Hamas.
I have a theory that the shell is plastic explosives that were mixed in that way you don’t need the battery to explode you just need it to provide enough of a charge to begin the sequence to ignite the plastic explosive…
I do realize plastic explosives and plastic are different but I’m sure with enough money in research they can figure out a way to make an inert hard plastic explosive