My Charge 4 stopped dead after 17 months. The diagnostics advised by the support tech were no different from what I'd already tried from these forums. The tech was somewhat condescending in walking through the recommended troubleshooting steps. Insisted on performing steps already tried, and failed to listen to specific concerns (NO green sensor lights flashing as they should be) that might have suggested different steps. When these basic steps did not resolve, he said the matter would be sent up to a higher support level, but what actually happened is it went directly to the automated message "it's no longer under warranty, here's a 35% discount to buy a new one". It feels to me like (even though it was no longer under warranty) complete failure within 17 months of purchase is unacceptable, particularly when it seemed like more targeted effort could have been made to resolve the issue. I suspect had I still been within 12 months (where a failure would have meant a complete replacement), a greater effort to get it running again would have been expended.
From reviewing others' experiences in the forums, this seems to be less helpful than is the norm for Fitbit. When I followed up with this message - within 24 hours - I received another automated reply that my case had been closed, since "it's been a long time since we heard from you".
Beware, the advice to 'contact tech support' might just get you more automated messages than actual support!
Moderator edit: updated subject for clarity
