Yes, that quick. It is probably leaded batteries do no like to get drained fully. I have two UPS now that dies as soon as electricity goes.
I am thinking of writing a script that will trigger the desktop to shut down as soon as the LAN goes down. My desktop is 1kw PSU, so, I am really not looking forward to replacing the 1.2kw UPS every few years.
These Laptops will be only doing backups, and small personal services
one for photo backups, replacing OneDrive
Another for sync, calendar service etc.
None requires heavy processing, in my knowledge. So thermals are not going to be an issue, hopefully.
Secondary issues are cats. And I don't have any idea how to stop them from stepping on the keyboards whenever they think like it, or jump on the router and cut the Internet :|