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I was thinking of creating a power management module myself that would have had a raspberry pi receiving periodic battery level readings and controlling a relay accordingly but the battery on the laptop was already messed up.
I don’t know whether it’s possible to recondition a messed up battery by managing the charge cycles.
Ssh with ed25519 pubkey access and password login disabled works fine for me. I have access from my phone via termux and any other terminal software.
As far as your changing ip goes, you could have a cron job that periodically checks your current IP and notifies you of changes over telegram or other method.