On my 4020's I just had a sheet metal box made with about two inch or so sides and welded it to the old brackets that the original box sat on. The battery is under the platform the way I did them. I wouldn't be a big deal to bend a piece of sheet metal that could be bolted on to cover the battery. On our old 4520's we have the battery next to the starter sitting on a platform with short sides. Probably should have tops over them for safety reasons.
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 IMG_1677.JPG (167KB - 562 downloads)
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John Deere 4020 add on battery box
