You might want to look into EcoFlow. I use their River system to provide backup power for my home equipment (I have frequent power outages, usually about 2 hours in length). I can't tell you whether it'll work for medical equipment, though.
I checked out EcoFlow a few weeks ago along with the Anker Solix range. Anker's switching times are around 20ms and I wasn't able to find EcoFlow's switching times. The switching times indicate the UPS performance. It needs to be quite low for sensitive equipments like a dialysis machines. The APC SMX range provides switching times of 4ms.