Assuming a lithium battery and control over the firmware+power draw, couldn't you theoretically make the battery output more charge than safe, leading to at least overheating and maybe more?
I also find it unlikely this was just a remote attack rather than supply chain, but with little to no details we can only assume for now.
Not really. This is about the worst your can do with a lithium battery in practice https://youtu.be/oieH2wwDGzo and that's a proper short in something way bigger than a pager. They don't explode like these were reported to.