My cranking battery is not hooked up to my boat's battery charger, so I just use my car charger to charge my battery. So, here are my questions:
Would a trickle charger be a better option?
And if so, do you keep the trickle charger hooked up through the winter months while the boat is in storage?

Thank you for your help!

I can't say if it's better to use a fast charge of slow charge for a cranking battery. I do know it's not good for a battery to just sit as it will lose it's charge and that's not good. I keep a Battery Tender hooked up to my cranking battery anytime it's going to sit.

Thank you Stump Finder!

I don't use a slow charger. I only use 10-15 amp chargers. My research has shown slow charging isn't the best. I don't leave the charger on because of the possibility of a malfunction and/or the water level getting low and damaging the cells.

When I am not going to be using the boat I make sure the batteries get charged once a month and unhook anything like a gps antenna that can draw current.

I leave mine plugged in 24/7 and check the water once a month. Never had a problem. Thank you Jesus!!

A trickle charger is the best when you are leaving it stored for long periods of time. Too much amperage will "cook" the water from the batteries.

Trickle chargers are pretty old technonogy. They will still cook your batteries because even though it is a low current, it's still steady whether the battery needs it or not. You really need a Smart battery Charger with multi-stage charging and a float mode. The newer one also check the state of the battery and do an equalization at specific intervals.

It depends on the dynamics of the charger. Fractional milliAmps should not "cook" the batteries.

Explain charger dynamics. Any charger source left unattended for long periods will eventually cook a battery.