I use the separator with the green knob you turn on my Bronco. 'Think Walmart has them by the batteries. I have one on the tractor too, but I'm so allergic to work, that battery still goes down.
Of course the Jeep (without a separator) owned by the lease partner that doesn't take care of a cotton pickin' thing he owns (trash in everything, always has to borrow something, etc., etc.) miraculously always starts. 'Guess it's all in your attitude.