The "It's certainly not a big deal and an easy fix" is a sentence I can't here anymore as I've heard it too many times when I had my own workshop (as well as my father when he was an independent mechanic, so nothing new here).
At the end, my answer was always the same: "Go on, help yourself, the tools are there."
And guess what the embarrassed answer always was...
If it's under warranty and you know nothing about electronics, but have done all you could do, which is putting a new battery and it's still not working, do what's been proposed to you by the store: Send it back and get it fixed.
This is what warranty is for. 😉