I like the more secure and permanent use of the "harness" that hyperV6 refers to. As a bonus, some things will actually plug into such a harness to be run on your battery power. For instance, I have a small tire inflator that has the same type plug, and instead of trying to keep track of a cigarette lighter/power outlet adapter, I can just plug it directly into my "charging harness" and draw power out instead of putting it in.
For the larger batteries out of my "summer" vehicles and for my trailer winch, I remove the batteries and put them under a bench in the shop on a piece of plywood. Easier to monitor, keep clean, and do any maintenance than if left in vehicles spread all over the place. Also ensures I'm always close to an outlet, which my trailer and ranch tractor hardly ever are.