This was the custom double battery set up I did back in the 80's
These was ok except I could never get to the middle battery plug to check the water level as the clamps went right across the middle of the battery.
So while the floor was out recently to upgrade the cabling, I fabricated a new clamp from 25 x 12 mm aluminum angle. A few pop rivets, a coat of black paint to blend it in, and bob's your uncle.
Very happy with the finished result