I have a Fountain with shore power and battery charger. In the past I have disconnected the batteries after charging them, then reconnected and charged again in the spring. I was thinking of leaving them connected and put the shore power on a timer to keep the batteries at full charge throughout the winter. Is this a good or bad idea? I shrink wrap and store the boat outside at my residence.

Pull the batteries and bring them inside. If they freeze one time the plates will short out and there done even if they are brand new. Unless you don't like the boat and have good insurance on it I wouldn't leave it plugged in.

I disagree, the cold will keep them in hibernation. Mine last over 10yrs mostly due to the cold winter in northern NY. Full charged, unhook, leave alone..

I usually only go 4-5 seasons on a set and then replace them. I just noticed this spring I'm on season 7 with the current set. I turn battery switch off and leave them in the boat hooked up. In the spring I put a trickle on them to top them off. They usually only show a tad down each spring.

As long as the battery is fully charged and in good condition then leaving it outside in the cold is not a problem, I found out the hard way a few years back and did some research on why they would freeze. Turns out if the battery is not properly charged or has a bad cell the acid will not be mixed properly and will separate from the distilled water....so they can freeze at 32*F just like normal water does! A good battery can go as low as -76*F before freezing so leaving them outside in the cold is not a problem.

Yeah i leave a thermometer in my boat over the winter that has a high and low temp recall. I think the lowest it read since I put it in the boat was -12. Batts were fine. Brrrr!!!!

I isolate the battery from the rest of the system by switching the battery switch off, I make sure the electrolyte is full, and hook it to a solar powered battery tender.

Battery is 9 years old now and lives on the Canadian border.

Boat fires right up in the spring.

Ken

Confirm the batteries are filled
Clean batteries with baking soda water mix
Charge batteries
Disconnect batteries
Leave in boat and forget
Been doing this for 30+years

30 + years ! they are really good batteries !!!

That's it ? Hah.