Sadly my garage is some way from my home and does not have a power supply. I have always envied those that can use a battery conditioner.
Best, Lol
There are solar battery charger kits available for yachts. I know it is not going to be all that functional when the roof is under snow but it may be worth considering.
Something like this would do the job
http://www.sunstore.co.uk/20w-12v-Solar-Battery-Charger-Boat-Kit.htmlYou could do something clever such as but a largish battery in the garage and hook up some 12v lighting too. Then wire in a cigarette lighter plug, preferably fused and with a switch, that you could then plug in to the car.