At this point in the world, just fuck literally everyone and everything.

Wired? Certainly.

Doing it without extra wiring is probably possible too. You'd have to override the battery charge controller, which is probably not available to an app, if to Android at all. But I'd be unsurprised if there was some exploit that made it possible.

I'm not an electrical engineer but I did work with explosives a little in the army. You'd only need a small amount of high explosive to do some serious damage to someone if their phone was in their pocket and that explosive went off. Modern phones have plenty of empty spaces to stuff full of enough explosives to do lots of damage. It'd be a lot easier to detect then just making the Li-ion batteries ignite but who can say what the IDF can smuggle into the supply chain.

No but I bet they could be used do melt the device, imagine if all of a sudden nobody had phones, chaos.