eermm , on the battery effect issue.... it does not take place when the two metals are in direct contact, think about it for a moment.... (but not to hard... OK
) for the battery effect to be able to damage either of the two metals, there needs to be a current to flow from the one, to the other, through the electrolyte. Now what do we know about electrical current, it always chooses the path of least resistance. It also needs a potential difference to exist between the two points of travel.
Ok so now how is current going to be able to flow from the one plate, through the liquid, to the other, in order to have what is called "the battery effect"
oh by the way I've been mixing metals for longer than Water-cooling pc's have been in existence.... heck Ive been doing it even before there was such a thing as a PC to be bought in a shop. In the HOT-ROD building arena, what we normally do to prevent this, is to electrically connect the Radiator, often copper cored, to the engine block, (Aluminum and Cast-iron in most cases) and in doing so we got rid of that exact same annoying phenomenon.