If your battery is 85 percent that's a good thing. Try updating your phone, if there's one available, if not call Apple. They will run a diagnostic and depending on what they find they may or may not charge you.
They will charge to replace the battery and the cost will depend on the battery you will need. They will also recommend turning some apps off, that are running in the background. If this is helpful please give me a thumbs up.
I don't think this is a question for this community, call Apple,
Thanks! Your answer is awaiting moderation.