I've been using an Odyssey PC-680 for about six years or so. It is tiny (weighs about 15 lbs), but despite that, cranks the low static compression, 3.3L with ease in temps down to about 30 degrees (never gets below that where I live - and only that cold on rare occasions), and has a surprising amount of reserve power; I've had "no start/hard start" situations a few times, and the battery doesn't seem to run out of cranking power more than a regular sized battery (obviously, not as much power storage as a full sized battery, but plenty for extend cranking situations).
It's a "power sports" battery and does not have automotive-style posts on it, but post conversion kits are available and inexpensive.
https://www.amazon.com/Odyssey-PC680-Battery/dp/B0002ILK6I/ref=sr_1_1?s=automotive&ie=UTF8&qid=1475468123&sr=1-1&keywords=odyssey+pc680
The only real negative is that it will run down quicker if a power drain is on it when the engine is not running - so that might be a concern. I've made a habit of leaving a trickle charger on it when parked at home - a good idea for any battery in terms of extending its service life.
It's completely sealed, so no risk of leakage, and can be mounted on it's side if you wanted to (mine is mounted upright, using a custom holder that I made).