[MrForbes]

A one gallon engine is the Buick 231 cubic inch (3.8 liter) V6. This I can remember.

And a pint is a pound, the world 'round. This I can also remember

so you need to displace two gallons of water (462 cubic inches, which happens to be a 1960s Lincoln engine) to make a battery float (8 pints in a gallon, two gallons = 2 x 8 lbs/gal = 16 lbs), and you need to displace more than that for the rest of the weight of your system.

you do understand about cubic inches, I trust.....just multiply the height times the width times the length (assuming a rectangular box) and you get the volume in cubic inches of your box.