Flooding destroys alsl batteries obviously, but the slightly important difference to Fukoshima is, a saltwater batterie does not contaminate the area.

Besides that most areas aren't in the risk of flooding, there is litte preventing you to water proof your batteries to the point that submerging them into water has no ill effects. The housing of the batteries usually is water-proof anyway. Just look at all the Teslas driving through deep water. Oil tanks for heating are a huge problem with flooding though, as they tend to leak oil into the environment.