Bill, top up at the Burlington WA supercharger just off I-5 four miles north of the State Route 20 turnoff to Anacortes. If you are stopping at Friday Harbor, no reservations are needed except for the daily FH-to-Sidney BC run (reserve; see the ferry web page at wsdot.wa.gov).
Allow an hour lead time except Friday, when allow 90 minutes at Anacortes. You can easily rack up 60 miles sightseeing on San Juan Island. Allow lots of time for the west side road looking over to Victoria and the Olympics, just to stop and hike down a ways. No Nav on that road as 3G coverage is from Victoria.
I will be on the Monday 11:50am sailing from Anacortes to FH, going up for a climate science faculty retreat at our marine research lab, all of the forest preserve with lab buildings that you will see on the right from the ferry when coming into the harbor. If seeing marine labs is your thing, I will be happy to walk you around. Otherwise, watch for an MS that is silver/pano. Returning on the 1:50pm Wednesday.
Plugshare has several 120v charging possibilities on the island, last time I looked. Lots of public chargers in Canada. Remember that September is still high season in the San Juans.