This is largely a misconception that's caused by the fact that EV fires are hard to extinguish with normal water sprays. That is because the bettery packs are designed to be water proof, so it is hard to get the fire patrol's water in. If you can immerse the pack in water, the fire is extinguished without much trouble. That's unlike petroleum fires, where the fuel is lighter than water and liquid, so water spray will boil and spread the fire instead of extinguishing it.

It doesn't need to be extinguished, it just needs to be removed from the ship. Even a second of airtime (and a healthy lateral velocity) might be enough that the ship is out of the explosive radius of the battery.