Re: 4d batteries
What type of battery is that, deep cycle, dual purpose, commercial/starting? I got a take-off 4D (8D?) commercial battery from one of my friends years ago. He worked heavy equipment and they swapped then in pairs, I got the good one. I used it for 1-2 years running incandescent fishing lights (high power draw) and it worked good, even though I was abusing it, it wasn't a deep cycle.
12.4V is only 70-80% charged, so those batts are not in great condition, if they are stabilizing at 12.4V, 12.7V is 100%.
If you can pop them in and run them, you don't have much to loose, but I wouldn't modify anything to "make them fit". Being that they are only holding 12.4V, I'd expect to be replacing them in the next year or 2,,, if they make it that long.
Those are heavy batts, probably 100-120# each
