[5540jd]

A battery maintainer would be a good addition to your tractor. Makes the 6V ones last much longer. I have a couple solar ones mounted to the south side of my barn, they do an excellent job keeping battery charged. Especially on one not used very often or driven long enough to achieve a good charge.

 

[5540jd]

That doesn’t look like a very big wire to me for a battery lead. The bigger, the better. More current capacity in a larger wire. And both positive and negative need to be the same size. Same amount of current flows through both.