My garage is probably over freezing even when it's 15-20 F outside. The battery hasn't died yet, even after sitting idle for a week.
I have a Battery Tender, but rarely connect it, even though I have the doo-dad connector hooked up to the battery with the connector accessible under the left cover (I have a Corbin seat which is a pain to take off.)
Battery Tender
They say it's great for the battery to leave the Battery Tender connected all the time. It keeps the battery from degrading.