Hospitals are categorized as critical care facilities, regardless of how much on prem compute they have.

Under national fire and electrical codes hospitals have to have at least three completely isolated power systems (these are the different colors of electrical outlets you see).

The life safety branch is the most critical and powers things like fire alarms, exit signs, stairwell lighting - anything required to evacuate patients.

The critical branch is patient care like ICU beds, ventilators, and operating rooms.

Lastly is the equipment branch which is essential to patient care but won't kill people immediately: HVAC, kitchens, and sterilization/cleaning equipment.

There is usually a fourth system for everything else, but these are the required ones. Each has its own requirements for battery and generator backup (life safety can't take more than 10 seconds to cut over), and usually the systems are wired so that they can draw power from lower priority circuits if needed.