That could be more of a problem. Regardless of the height, dumping a battery means a projectile falling, which could injure someone or cause property damage.
If fuel is dumped high enough, it pretty much evaporates and doesn't fall to the ground. If the plane is low when it dumps fuel, it can hit the ground and bystanders; but, it's not going do much, if any damage. (Assuming it doesn't hit someones barbecue or a smoker.)
Or alternatively, if a plane develops a leak in one of the tanks, it can dump fuel to balance the weight.
Is there a scenario where a plane in flight has its fuel on fire and dumping said fuel helps in any way?