Hardware question

I recently started a home server (HA, Jellyfin, and Pihole) using an old laptop with a broken screen and a faulty battery. I removed the screen and battery, so I do not have power backup (core information to my question). Since it is a laptop, the BIOS does not have the option to turn on when power is detected. In the case of a power outage, how do I force a startup? Additional information: I'm planning to 3D print a case and move the motherboard, and it won't have the keyboard after that.