Same problem here with my mini - it can barely get through a day now. Do you know if you can walk to an Apple store and ask to just replace battery?

I have iphone 11 and you can have battery replaced just fine. I did it few months ago and the phone became like new. I am not sure about Apple in US but if they won't do it then some third party will.

I've had good luck with my local Apple store replacing batteries in older models. I made appointments rather than walk-in.