I think I may be able to help in this regard. Certainly the minimum battery weight is required to satisfy logitudinal stability requirements. However a maximum battery weight is also set as if the battery is too heavy it will reduce lateral stability by moving the COG too far to the pointy end of the stability triangle. Shorter trucks have a shorter stability base and thus less tolerance to affects on their COG. Thus shorter equipment usually requires less counterweighting to maintain lateral stability. I dont know all the details but I would say this has something to do with it. Crown should supply you a minimum and maximum battery weight.