Originally Posted by avanti
It is not a good idea. Fully-disconnected batteries of any commonly-used flavor will maintain adequate charge for many, many months without the slightest issue. A trickle charger accomplishes nothing, and has a (small) chance of malfunction.
Also, if you are storing the vehicle is a sealed container, beware of the accumulation of outgassing from a battery on a charger.
Agree, especially if AGM as they will normally make a winter storage and not be down more than maybe 20%. Wet cells, especially if older, may get into an issue and be near going dead, though, especially starting batteries that probably are at only 60-70% most of the time.
I also would not have a charger on any kind running in small closed area, just plain bad idea with stuff that can go wrong. Perhaps, if charging were necessary, having a cord in place that you could open the door and connect to would work to occasionally charge, with the door open, could work out. Only if you need it though.
Most sealed containers are usually not totally sealed against temp swing "breathing" of air in and out, so you can get a humidity build up in them besides. We ran into this when using containers to store overproduced products at a place I worked. This was in Minnesota. Even an insulated, unheated, container will eventually wind up at the average of the outside temp, so if the is below freezing, the unit will freeze inside.
I think, personally, if I were going to store in a container, I would use one that that had ventilation and just count on things freezing inside, but it would stay dry that way. Freezing is not an issue in most cases.