The mechanism of storage makes all the difference. If I store my Joules as, say, wood that has dramatically different failure mechanisms than if I store it as RDX. Even if the difference is just diesel vs. RDX. It's easier to prevent an explosion hitting diesel fuel from destroying a ship (it's been done since WWII) than it is to prevent an explosion hitting a stockpile of explosives from destroying a ship.

Even more so if the energy is coming from a fission reactor. Since the energy source is comparatively more compact and can be protected with armor more effectively.