I tend to agree with Larry. But I have put an electric heater in the boat, under the cover. Run the cord through and hooked firmly to a cleat, so it can't be pulled over by tripping on the extension cord. Use a heater with a shutoff switch in case it is knocked over, and don't turn it on real high. Most extension cords are not big enough for that full throttle amperage, but at low setting, they're ok with the fan blowing. I used one of those grey heaters from Costco.

Glenn, there are batteries that LOOK like there are no caps, and then there are batteries that REALLY have no caps. That's why I like Delco Voyagers, and they last a long time, because you can't boil them dry. All you have to do is run a battery low of water once, and it's toast.

The thing that worries me is the whole.."Boat Burning Down" issue with leaving lights or lamps around...

What I do with my boat that has to sit outside is, I take one of those cheap Heat lamps with the deflictor shield on it and lay it in the middle of the floor. That , with the cover and tarps the boat stays perfictly dry. Also I run a drop lite into the battery box which keeps the battery box warm and from freezeing. It's a fact, that if your in a small space (like trapped in your car) and you can keep a candle burning...you won't freeze to death.

                                   2 cents

Good points Larry.  What about those folks that have "no maintenance" batteries?  Mine are like that - there's no cap to remove or any place to add water.  It's completely sealed.  Does that mean they're ok, or is there some way to check?

Adding to the tips, always store you boat with the front jacked all the way up and the plug pulled - especially if you store outside.  Any water left in hull (like from rain), could freeze in these temps and cause rivets to pop, or even stress cracks in fiberglass. 

Also make sure your engine is drained completely of water before putting on the transom saver and trailering the boat home.  A lot of damage could occur if water freezes inside the engine.

Saturday although cold, looked like a good day for a little fishing on Sawyer. I prepped the rig, added oil, had it on charge for the last week, and you would think that since I had checked the water in the Batteries a month ago.....they would be fine today.......see where I am goin with this?......At the launch I went to raise the motor off the stand and.........just a buzzing sound.......again....a buzz.....thinking it was a frozen hydraulic ram I tried the ignition........end of fishing this weekend...........
Moral of the story.......I learned that in cold weather especially Freezing cold.....charging and cold exposure can both boil and freeze dry your battery so keep up on the fluids......while on this subject....How many of you drink water on cold days? The wintertime is one of the worst times for Dehydration and combined with the flu season can debilitate you from your fishing excursions so make sure you get at least one or two liters a day of JUST WATER! Thats our Maintenance and Medical tips for the day!......p.s.......Being stuck at home caused me the biggest pain of all........having to sit at home and watch the Huskies upset the Cougars.....BAD DAWGS!!!.....BAD DAWGS!!