You don't. If it's an electrical fire you'll smell an acrid smell from a mixture of swamp gas and hydrogen gas from the insulation burning and while bad, you can turn the battery off, close the vents putting out the fire, then reopen the vents and safely land while praying it's not night time.
>electrically propelled aircraft
Don't know. I'm looking up the physics of how this works and all I'm getting are new-age PopSci articles about how "batteries will improve enough to handle electrical propulsion" (they won't) and how the "science is already there" (apparently it isn't since nobody can describe how these fucking work and they don't sound like an air pump since I wouldn't think an air pump would be strong enough), or how there's "150 companies developing electric propulsion aircraft" (but nobody has a working prototype).