My Mom has a 7 with the latest version of iOS. Never had to replace the battery for some reason (she’s very easy on it).

I often use it when I’m around her for some reason or another. Works fantastically. My only complaint is that between the smaller screen (compared to a FaceID phone) and her having it in zoom mode (easier for her to read) the screen feels cramped.

But performance wise it’s not an issue at all. Nice and smooth. She’s not playing high end 3D games or editing video so it works for her.

Only reason she’s thinking of upgrading? The cameras have come a LONG way in 5 years.