That's a hilarious observation, and I've upvoted it.
However, batteries (as opposed to capacitors) get their power from redox reactions. If we use a definition of "fire" that includes the rapid redox reaction between liquid phase propellant and solid phase propellant in a hybrid rocket motor in the vacuum of space, that definition would likely also extend to rapid redox reactions between liquid electrolyte and solid electrode in a battery during a particularly fast thermal runaway in the vacuum of space. In other words, under many reasonable definitions of "fire", any sufficiently rapid thermal runaway in a battery would be a fire, despite there not being any air present.
However, batteries (as opposed to capacitors) get their power from redox reactions. If we use a definition of "fire" that includes the rapid redox reaction between liquid phase propellant and solid phase propellant in a hybrid rocket motor in the vacuum of space, that definition would likely also extend to rapid redox reactions between liquid electrolyte and solid electrode in a battery during a particularly fast thermal runaway in the vacuum of space. In other words, under many reasonable definitions of "fire", any sufficiently rapid thermal runaway in a battery would be a fire, despite there not being any air present.