Maximum, or current health? That is an important distinction which can drastically change the armor's utility.
I kinda did that for a boss. They had to call shots and destroy body parts doing at least 25 damage a turn or it healed. Turns out level 13 5e PCs have no problem with that.
I guess the technical answer would be "all of them"? It's some Dall-e 3 images muxed together, not a real game... ;-)