The size of battery for a Massey Ferguson 35 Diesel Tractor depends on the specific model year. Generally, for tractors made before 1970, the standard battery size is 12V, 6–36 Amp Hour. For tractors made between 1970 and 1975, the standard battery size is 12V, 65–95 Amp Hour. For tractors made from 1975 onwards, the standard battery size is 12V, 95–145 Amp Hour. It is important to replace the battery with the same type or an equivalent as specified by the tractor manufacturer to ensure proper functioning.