So I only drive my car about once every two weeks, and I am finding that my battery is starting to no longer hold its charge even after fully charging it with my Battery Tender in between drives. The battery is only about 1.5 years old so I think my bike commuting is killing it. I don't like having my BT hooked up all the time because it is essentially entirely outside my condo except for the extension cord and theft is pretty frequent in my city.

Are there any good car batteries that are spec'd to hold their charge for a long time with infrequent charges? I'm willing to juice it all the way up like once or twice a month with the BT if needed. It's just annoying that the rare times I need to use my car, it hasn't been available to be driven until I charge it up overnight.