Greg,
Interesting, you didnt get the spike before the tank...
I have missed the battery change twice. You have 7-10 days after the warning indicator comes up the remote.
In my case, the pressure rose to a near impossible high over a few days, then quickly fell to around where you ended up. There was still enough juice to connect to console so for me at least the issue was not at WU. I think they just propagate the last sent value.
Andrew
ps: The irony of the battery change indicator is that I have had extra sensors last a few months to a few years on low battery with normal results, but the internal one no likey the the low battery.