The reason we don’t see exploding battery attacks more often is not because it’s technically hard, it’s because the erosion of public trust in everyday things isn’t worth it.
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.
Even though your edit clarified it, I wish we’d stop calling them “exploding batteries”. The battery isn’t the explosive, it’s the explosives that were hidden in the device. I’ve already encountered far too many morons describing conspiracies where the big bad government could make your iPhone explode.
And if we're being pedantic, when a bomb explodes, so does everything around it. Exploding doesn't require a chemical reaction. It's the act of tearing apart quickly. So yes, the car exploded.
That's in English though. Other languages may be different.