I live in an apartment which makes it difficult to use a battery tender. When the temperature drops below 35 for a couple of days, my batter, even when new, will not hold a charge more than 3 days.
Until I started putting the cover on her at night. Kind of like tucking in my boys when they were younger. I do have covered parking, but no garage, so it seems the cover helps keep the freezing temps from draining the batter overly much. Started fine today with no jump or charge.