I think your battery's shot or insufficiently charged. It doesn't matter that it's a year old, lots of year old batteries fail. When they go, they go.
It isn't healthy to have the battery off a maintainer all winter, nor is it good to leave it in the car. The battery can drain and 'sulphate', reducing the surface area of the plates, resulting in less power storage, and more work on your charger or alternator to charge, which for the latter will also reduce your MPG.
A good schumacher maintainer can be had for $20-$25 and will cost less than $5 to run it continuously, which really isn't necessary. I have 2 car batteries and 2 moto batteries on my bench all winter (5 mos.) in a garage which avgs. 35°, but rarely drops below 30°. I use one maintainer between all 4 batteries and swap the clips each week from one battery to the next throughout the storage period. All the batteries are at least 3 yrs. old (oldest is 7 yrs.) and they are all healthy. As mentioned, have it tested and correct as necessary.
