Small Battery.

Try Battery Mart low prices and fast service. Bought my PC680 for my 350. NO PROBLEM with starting.....

 

I've always liked Kinetik batteries, but that Odyssey seems to have a stout reputation.

I use them for OT stuff, but here's a link if you're interested:
http://www.kinetikpower.com/2009/product.asp?C=1&P=KHC600

Dimensions: 7"x3"x6.5"

 

They are an Absorbed Glass Mat type of battery. They are sealed and can be mounted on their sides if you need to.