I just pulled my boat for the winter...

[Cliff]

I just pulled my boat for the winter (I live in the Boston area).  I typically pull my batteries (3), put them on a trickle charger and reinstall them in the spring.  I see both schools saying take them out, leave them in. Why pull them out?  I don't do that with my car.

[wingless]

A battery should be maintained above 50% state of charge to limit the sulfation permanent damage.

A battery state of charge drops about 10% per month.

It is unlikely that a long winter layup will permit proper battery storage w/o topping off the charge.

[Hugo]

Wingless also offers sound advice.
I'm in NW NJ and store my boat outside for the winter. It is well covered and protected but I take my batteries out and store them in my furnace room -off the concrete floor - in my basement. starting in March I trickle charge and it has worked well for 1for me for 8 years.