Battery options BESIDES Optima?

I found this setup today on an experimental airplane. They are using Odyssey PC680 batteries mounted on their side under the floor. The batteries are only 3 " wide, 7 " tall, and 7" long. They are mounted in series for a 28 volt system. I haven't looked up the specs on the batteries, but they are cranking a 540 cubic inch Lycoming engine with a 10 foot cable run. I was impressed.