I would suggest that you install a heavy vechile type isolator switch into the battery leads. We placed our isolator switch under the batteries and above the RH rear wheel [ R62 ] where it is very convenient and can be immediately accessed in case of fire or can be easily reached to isolate the combine electrics when welding or just leaving the machine overnight or for longer term storage. Agree with Dan on the fire precautions. Always have somebody else present if welding in areas where there may be straw residues around to catch fire as you may be concentrating on the welding and not realise that the combine is lighting up around you! We have hoses at the ready and a pressure water or foam extinguisher at hand as well. When welding with a lot of straw residue still around and in the shed, we usually try to have a quick way to get the combine out if it starts to go up so we don't lose everything else as well. A lot of Aussie farmers now own engine powered 100 CFM mobile industrial compressors to blow their machines down at the end of the day or for any maintenance such as welding. Wouldn't be with our ours. Cheers!