Like Kenny says, the only safe thing to leave on your battery all winter is a float charger. A trickle charger will ruin your battery. Slow overcharging will eventually dry out the cells. You should fully charge your battery with a normal battery charger before storing it whether you use a float charger or not. Whether you remove the battery from the boat is up to you, but removal is safer. You should disconnect one of the battery terminals if you leave it in the boat just in case there's a parasitic drain somewhere.
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