Technical Converting to 12 volt

1931 ford hot rod W/ 239 flathead changing to 12 volt. What is the best group number battery that will give me the best fit.
Thank you
Chris

 

Get a tape measure and go to an auto parts store that has a battery display, or look on the internet for a battery size chart. The info is out there.

 

The best size is the one that fits in your battery tray/box.

 

If your A uses the group 1 6 volt battery, the group 59 battery fits very well. That is the battery I use when convert old Farmall tractors with completely enclosed battery boxes

 

i just take my battery box to autozone (believe it or not) and they always find something that works!

 

And has the terminals in the right place.

 

I personally like (some people don't) side terminal batteries because of better resistance to terminal corrosion. I went to side terminal on my truck and my '55 Ford. As others have said, measure your battery tray. Not hard to find a battery that will fit a tray that was designed to fit the common Ford size 6 volt, use a universal replacement hold-down from the parts store.

 

I have converted two old Ford tractors, an 8N and an 850, and a Group 35 12V fits the original battery box very well