I just put the boat battery into my heated garage for the winter. It has removable caps so I topped up the water such that the image was “ upside down” inside the cell. I’ve topped up each year at the end of the season. The battery has been sitting outside disconnected for the last three weeks and still had a good charge on it. The CCA was just a bit lower than spec, at 620. I know lots of people like trickle chargers but I just charge it at Christmas and Easter with a smart charger. I also give it a charge after each run, as the kids often listen to the stereo. Six seasons now and still looks pretty good.