I keep my (3) trolling motor batteries hooked parallel to a 1.5amp trickle with auto shutoff all winter. I also keep them on a shelf in my garage. Makes it easy to walk by and see if the "red" fully charged indicator light is on. It (the red light) is usually "on" all winter once the batteries have fully charged since there is minimal drain over winter. Seems better to me than leaving the batteries in the boat out in the freezing cold and never seeing the charger. It's also just a good excuse to empty the boat completely out once a year for service and inspection. I would hate to open my boat up in the spring to find battery acid has damaged everything in it's path from a leaky battery.

2 cents worth......