I have a marine battery for my boat. the terminals have some corrosion on them. can i file the corrosion away an rub some grease on before applying all my connections again?

A solution of 1 part Baking Soda and 2 parts Water is one method of removing the corrosion from the battery posts. Once cleaned (be sure to thoroughly dry them, too) apply a light coating of Vaseline before re-connecting the wires to the terminals.

Never, ever, use soda for this task ... the sugar in the soda leaves a residue on the terminals and makes them sticky.

I have found it usefull to put silicone sealant around base of terminals . this helps retard acid fumes from causing future corrosion. it may not stop it but it will definitely slow it down. P.S. I do it with all my batteries with top side terminals.