After a long hunt involving the Washington Attorney General's Consumer Protection Office, the Washington Law Library Research Service, and my local State Representatives research assistant, the answer is that Washington adopted SOME of the California CARB rules, but did not mandate the extended warranty for the battery pack. It was a lot harder than it should have been to get a straight answer to a seemingly simple question.
Yesterday I had a refurbished battery installed by a mobile service right in my driveway in under an hour, including the tech taking the car out for a test drive after clearing the error status codes. He then had me take a quick spin while he filled out his reports (on-line, of course). The lag in acceleration I was experiencing with the failing cell in the original pack was gone and the battery topped up it's charge very quickly. The refurbished battery has a lifetime warranty covering future cell failures too. (And the company has been around long enough that I'm not too worried about them disappearing suddenly.) I called the company in question on Tuesday, and they scheduled me for Saturday - very nice. Total cost - $1695, which included the installation.