The batteries have breather valves. If subjected to enough pressure, they can lead to water ingress. Despite Musk's statements, submersion isn't recommended. I

The batteries have breather valves. If subjected to enough pressure, they can lead to water ingress. Despite Musk's statements, submersion isn't recommended. I have never heard of one failing from a puddle or just "rain", though. It makes me think there is more to this story.