Im not a wiz on this, but from what I have read so far In a Tesla each individual 18650 battery is wired into a pack, each pack has a protection circuit that will shut the pack down in the event of a short, overheating, undercharging / overcharging etc, each pack is wired into a stack which also will have a protection circuit that will shut down a pack, in the case of getting wet it will just shut down the batteries from completing a circuit.
https://www.laserax.com/blog/battery...s-battery-pack
Pretty sure the Tesla battery pack has water flowing through it to keep the batteries at their optimal working temp.