Matt Ferrel did a video on NDB on his Undecided channel. Looked like good tech for niche applications, and while it'll last forever, it produces far too little electricity to be useful for a most things - in the realm of micro-watts. You would have to stack up a LOT of them to power an EV, think of it like trying to power a car with calculator or watch batteries. Sure it's doable, not sure on the practical. I wouldn't mind a calculator that never needs it's battery replaced, although solar has mostly made this moot anyway.
Beta radiation can be stopped by very thin shield of aluminum. In an intact battery, radiation will be a non issue. While I'm a proponent of nuclear power, I'd rather not have random uncontrolled radiation sources running around. Some retard will try and cut it open to get at the diamond for his girlfriend and leave the radioactive bits laying around for their toddler to stick in their mouth. Or the grinder they use to cut it open will powder some of the radioactive materials, to then be inhaled by everyone in the area. While clothing will stop most beta radiation, having a radioactive particle lodged in your lungs for years will be very bad news.