Best management practices for winterizing boat batteries

There are dozens of opinions about how a boat battery should be treated in the offseason. Some say just top off the charge and pull the tarp on Ol’ Wavewacker. “A fully charged battery is freeze-proof to about 90 below zero,” they say. “Even the U.P. doesn’t get that cold.” Some people say, “Just hook a trickle charger to it and come back in the spring.” I’m sure it works for some, but certainly not for everyone.