It’s worse when you’re at home, but asleep.
The fumes of a fire can suffocate and/or poison people in their sleep.
One way to do something cool with many old phones is just to run postmarketOS and play around with that. Even if the phone isn’t well supported, there’s still some to be had without it necessarily becoming a daily driver.
Many phones don’t boot without a battery.
Leaving it in is not an option, battery fires are rel and they are dangerous.
Also, a Raspberry Pi 4 or 5 is much better suited to be a server. I’ve got a Raspberry Pi 1B that has been runing continously since 2013, except for the few times I moved or did maintenance on my UPS. The 1B is not fast, but it only does light stuff, so it doesn’t matter.
It’d make more sense to continue solving the issue on the issue, not here.
Especially with people mostly scrolling past without reading into the issue to understand it.
Try Prosody or ejabberd. Easy to set up, needs next to no resources and works very reliably.
It seems like you need backups, so perhaps just add backups?
Also, it could always happen that a bug breaks your file during sync.