All the apps in the world won't help if you've got no signal!
I use one of these:
https://oceansignal.com/products/plb1/
It's tiny, weighs next to nothing and is my get out of jail free card......
Also take on remote hikes and ski touring where we quite often have bo cell signal
If I were in your shoes AND at the YT Mill after they'd just confirmed your diagnosis I'd be screaming and shouting in the middle of the showroom until they gave me a replacement battery.........
Not Specialised I know, but I just changed the Shimano chain on my Decoy after 1400km <5% with a chain wear tool and straight away it started skipping on the smallest cog (11t), disappointed as I thought I was doing a good thing!
So now fitted a new XT cassette as SLX out of stock here and a...
Just fitted a new chain and unless I'm missing something, the chainring is symmetrical, ie it doesn't matter for the placement of the chain as on a narrow/wide chainring?