Quite an explosion if a 1 kg battery developed a mechanical cascade failure and released its 1 MJ in a few milliseconds. That's about the equivalent of 250g of TNT - approximately 5 hand grenades worth.
If this concept pans out, that means that ceramic vacuum tube batteries could also end up being extremely rugged. As long as the final sealing of the ceramic didn't turn out to be a problem with the heat. This could circumvented by maybe sealing it with a laser.