Mine's a little smaller than Mike's, above.
My battery is an Odyssey P680 500-amp-starting, racing-style battery mounted in the nose of the car in the forward well of the trunk. It sits just forward of the gasoline heater and I needed something small (with specific dimensions) to fit the limited space. IIRC, I paid around $160 bucks for it and they're available through Amazon Prime. I keep it on a battery tender whenever it's in the garage. Shown below, it's the little red box at the bottom.