On a military version, where you haven't replaced the starter, and the batteries have to stay in series for it, why dont you guys just take out the resistors and run a separate feed from the + terminal of first battery to the relay. That way one or two open plugs won't raise the voltage to the remaining good ones and kill them off one by one. IMO any way you look at it the resistors are a dumb design and anything you can do to get rid of them is better, even if it means running your GPs off of one battery until you can afford to replace the 24 volt starter.