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I do not have a heated shop but keep them in the shop and even I replace batteries from time to time, but I have noticed to keep them charged if you are not driving them daily has helped quite a bit for keeping batteries longer, especially in the boat over the winter charging them either once a month or once every couple months the batteries seem to keep better.
Little trickle charger, or something a little beefier? I'm sure I can manage to park in front of the garage and snake an extension cord out.And I'll definitely be picking up a portable jump pack, those things are convenient enough to justify the price