Hey RIODOG. The electrolosis is caused by the fact thet electricity will find the easiest ground and in water it will take the " FORGIVING METAL ". This is why ocean boats will always use a zinc or in some cases lead plugs situated somewhere under water to absorb the electrolosis created by a boat seating in a ungrounded atmosphere. As a daily but that drowns and sits under water for any length of time. At which point the alumium becomes the forgiving metal. And You are very right I have never heard of an intearnaly fused battery.