PSE's analysis of batteries is badly flawed.  

PSE assumes batteries must act exactly like the transmission line, even though that isn't required by federal reliability standards.  That assumption makes batteries too expensive and too big to be charged in a reasonable time.  A good battery can increase reliability and save ratepayers a lot of money.

Why would PSE use a questionable assumption to disqualify batteries?  Because the company can make more profit from a transmission line.

What if we turned the tables and required the transmission line to match the advantages of batteries?  Then the transmission line would have to preserve thousands of mature trees, reduce carbon emissions, and reduce risk of pipeline explosions.

A transmission line can't do those things.  Batteries can.