I’m running a Ubuntu server on my old laptop with an external HDD connected to it. The external HDD is powered independently from the laptop, as it is plugged into the wall.
During a power outage, my laptop remains operational due to its battery, but the HDD shuts down. When power is restored, my laptop does not automatically remount the HDD, and I have to reboot the system manually to access it.
Does anyone know how I can resolve this issue?


Could you please elaborate on why this is a bad idea?
Having a battery that is constantly charging and kept at 100% is bad for the battery. Very bad. Batteries don’t like heat, and being kept on and in use endlessly generates heat constantly. Batteries should be avoided for things like this as they can swell and/or explode.
Chill bro they have BMS’s. I keep my always plugged in laptop at 60% battery for this reason but they aren’t infants you don’t need to baby them.