Hmmm, battery repair, as in chop pitch out and replace posts and cell connectors? If so, what dark secrets have you that I need to know? I haven't been able to find a repairman since 75.
OK, tractor battery box = multi step process or wasted effort.
1, soak box in clear water, heat optional to leach sulphuric deposits & salts.
repeat till water is clear. If box can't be submerged load with wet NEW catlitter and heat gently, no hotter than 200°.
2, After soak returns clear, I'd chelate the box in molasses. Chelation will remove oxygen from any salts left in the metal without damaging the metal.
Unfortunately you will probably have holes where the box is already rotted.
3, when clean drown the inside of the box with asphaltic roof coating diluted with mineral spirits, preferably allowing soak time. Let asphaltic coating dry slowly.
4, topcoat with Rustoleum
The electroplating process would NOT be my first choice due to potential tank contamination by the acid salts. It takes damn little acid to ruin a tank charge as I've learned from rainwater.
Base neutralizing acid salts in steel is damn near impossible, doing so requires heat, time and strong caustics, such as the old hottanks engines were cooked in before EPA.
There are a couple other tricks, but I ain't at liberty to divulge them. You know where the Guru lives, and if he wants to tell you he will.