If we can miniaturize nuclear reactors to the point that they can be drop-in replacements for batteries, then we can potentially run our electronics, appliances, machinery, vehicles standalone for decades without refuel/recharge.
The material is expensive (though it could be made much cheaper if a big market showed up), but more seriously it's a radiological hazard. Someone could disassemble such a thing and blow it up on a busy street with conventional explosives and cause a massive radiophobia-induced panic. You don't want to inhale a strong alpha-emitter.
I had heard these used Strontium(/Yttrium)-90 (β), but I might have been misinformed. Do you know where I can find more information about this subject?
https://en.wikipedia.org/wiki/How_I_Ended_This_Summer
It's a beautiful and grim piece of Russian film making...