Jane, I have the same problem every winter, especially if I don't use the bike for a week or so
It seems to me that these modern batteries aren't too good at handling the cold we've been having, so I wouldn't sweat about it for now
If you can't rig up a trickle charger, I afraid you'll just have to charge the battery when it goes flat, like what I did. I got pretty good at taking the battery off and carting it back to me flat
