Took it into the dealer expecting to need a new fob, programming and key cut. They changed the battery again, now it works and they charged me $0.
No idea how this happened - battery type correct, polarity correct, new batt voltage 3.2V and I tried 2 different ones???
Feel stupid but Kudos to Camp Chevy in Spokane. Hope this helps someone else, I'd plan to change the fob battery every 3 years at most.
Now once I find a replacement L1 charger I'll be a happy Volt owner again.