I would say the warranty is probably confidence that a percentage will last that long, and the amount they have to replace is cheaper than the business they lose not offering it.
edit: and no argument that companies are also working to make devices less repairable, i’m cynical that more often then not they are trying to design devices that last exactly as long as the warranty.
make sure it’s configured for clean shut downs before your battery runs out, auto power up on restoration, and hope it doesn’t happen. you will eventually have an outage that outlasts your batteries.
I have a large string of batteries from an old telco office, that runs my rack for 14hrs (calculated, I shut everything down around this time) and that did not last for the 2-3 day outage we had after a storm. Without a generator, you will inevitably have an outage, but if you are prepared, then you can mitigate any damage. use NUT if you need to shutdown or power multiple devices from one monitored UPS