You might also check into Dyna batteries, they are made right in Seattle, they are located right near the Fishermen's Terminal, on the Magnolia side of the Ballard bridge. (on one of those cross streets between W. Emerson and W. Commodore Way)

Directions:
If you're on W. Emerson heading west from the 15th or the Ballard Bridge, go past the Fishermen's Terminal, through the light at the Cafe Apassianato, and up the hill, take the last right before the bridge over the train tracks, go down that road almost all the way to W. Commodore Way [1/2 mile or less?] Dyna batteries will be a on your right on that road, it's a long, low slung building.

They cater to the commercial fishing business, so I'm sure they must be tough batteries. I've heard of people going to their factory there and getting good deals, though I've never bought a battery there myself or used one of theirs...

-N.