Yes, agreed. The problem is that some people, obviously not the intelligent variety who populate this forum, think 12v is full and that 0 v is empty.
Yes, an expanded scale type is very useful, but no substitute for a device which actually measures capacity.
I thought most sounders and chart plotters had a voltage read out which is infinitely more accurate that a voltmeter.
I really can't see carrying a hydrometer on board and I hope most of us use sealed lead acid anyway!