PSA: Check the backup battery terminals before anything else
I spent a whole shift in Denver convinced a panel was bad because it kept dropping the cellular link every 40 minutes. Turned out the backup battery terminals were corroded and the system was silently rebooting whenever the charger hiccuped. Anyone else ever blamed the panel first and found the cheap fix was just cleaning those posts?
Had the exact same thing happen at a site in Aurora last winter. The cellular radio was dropping out every 30 to 45 minutes and I swapped the panel after two trips out there. A tech I used to work with told me he saw this all the time on older systems where the battery posts get that white powdery junk on them. The charger kicks on and off, the voltage sags for a second, and the board browns out and reboots. So the panel looks dead but it's really just the battery connection failing. Now I hit those posts with a wire brush and some contact cleaner before I even pull out my meter. Takes five minutes and saves you a whole day of chasing the wrong problem.