Guessing they compromised the devices with a firmware backdoor, perhaps to remotely trigger an exploit that heats up the devices battery to dangerous levels once a signal is received. Paranoid about this happening with my vape mod with two 18650 cells
Could be true but that requires a lot more steps. Need the materiel to be implanted, delivered to targets, then have a software payload execute, instead of just the last step. However, most battery packs for pagers im seeing are 650 mAh which isn't much energy at all. Two 18650s have almost ten times as much capacity, and they don't explode.
That's enough to vaporise about 100 g of water according my back of the envelope calculations. Overkill? Or is modified for an entirely different purpose?
More likely this has nothing to do with the batteries and this batch of pagers was physically intercepted and rigged with actual explosives. A very concrete example of a supply chain attack.