Tom Walker wrote in a message to Roy J. Tellason:

-> You may find that in the case where there's a 35 in there you have
-> room for a 24F.  And where the 75 is,  it may fit a 78.  It's only 
-> needing one additional inch,  after all.  Me,  I kind of prefer to 
-> go with the biggest physical case that will fit in there.  The 
-> reasoning beind that is that to stuff similar capacities into 
-> smaller boxes they have to make the plates thinner, which is going 
-> to make it somewhat less rugged over the life of the battery. 
-> That's why I had a 31 in my old truck,  because it'd fit.    And 
-> the truck I have now has a 24 in it,  pulled out of a car I used to 
-> have and bought new for that car.  I only need about 350CCA or so to 
-> start that motor,  and it's a 525, so I should get at least 5 - 6 
-> years out of it,  especially considering that I don't run that truck 
-> all that much.  When it comes time to replace that, I'll probably 
-> put a 27 in there (12 inches long) unless I can fit a 31 (13 inches
-> long)...

TW> In the "Old Days" when I drove older and sometimes Harder Starting
TW> cars. Not to mention ones with quite a bit bigger engines, Untill I
TW> got the S10 PU with it's 4.3 L engine the biggest I have had since
TW> I had a Buick V-8. Most have been between 1.6 and 2.4 L. Anyhow I
TW> liked to do the same thing. I would measure up the space for the
TW> battery and carefully check the charts and get the largest CCA
TW> battery I could squeeze in there. 

Now I never went for highest CCA,  that's not what I was saying there. 
Biggest physical battery,  though.

Take for example that truck that had the group 31 in it.  Those were
available in three different ratings,  one was about 600CCA,  one about
700,  and one 900.  The one in the middle,  though,  was rated at 180
minutes of reserve power,  while the other two were only rated at 120
minutes.  The difference is thicker plates.

Some of what Exide made was designated as "EVB",  for Emergency
Vehicle Battery.  These were standard sizes but with high reserve power
ratings.  I also had good luck putting them in stuff that had diesel
engines.

Late-model dodge trucks with those used one single group 31 battery that
they rated at over 1000 CCA,  and I couldn't get one rated that high.  But
I recommended the one in the middle mentioned above and never got any
complaints.

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