edit: after 20 comments, i’m adding a post description here, since most of the commenters so far appear not to be reading the article:
This is about how surprisingly cheap it is (eg $15,000) to buy a complete production line to be able to manufacture batteries with a layer of nearly-undetectable explosives inside of them, which can be triggered by off-the-shelf devices with only their firmware modified.
The attack hit many civilians. For militaires it might be feasible to secure their chain. For terror attacks, which this was, it would be far more difficult.