Help with Battery Terminal corrosion and why

On the towing issue, when I flat tow my Ranger on the tow bar, I disconnect the battery, since it also needs the key in the run position to keep the steering column from locking.

I use a seperate, portable towing light system that connects directly to the truck I tow the Ranger with, so the Ranger does not need any battery power going to it's own lights while being towed.