I don't see what a difference the battery case would make. Haven't batteries had plastic cases for the last 50 years? I suppose there is a better kind of plastic being used now. But batteries are lighter than they used to be. I recall getting a battery at K-Mart that had a bunch of white plastic pellets, like styrofoam. I was told that this was because there was too much room in the battery, what with the thinner plates. It was a crappy battery (Exide, I think) and lasted only two years in a Hyundai with no serious accessories.
Have you noticed that cold weather energizes batteries? I have noticed the opposite: when the battery is cold, it has a lot less energy. Could it hurt to put a battery on a board? Again, I had a good battery and put it on the concrete floor of my shed. One month later, it wouldn't take a charge at all.
Semibodacious Transmogrifications a Specialty
1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)
"Time flies like and arrow, yet fruit flies like a banana"