Peak performance capability
I wanted to know if your phone doesn’t meet the battery performance, does that mean your battery is spoilt or needed to be changed?
Question marked as
Apple says that if the maximum capacity percentage in Settings>Battery>Battery Health is close to 80%, the battery should be replaced.
Sometimes, if the battery is reaching that critical point of its life, it can have unpredictable behavior and it's better to have it replaced in advance, before it dies completely.
I suggest that you create full backups of your device on a regular basis.
Regards
Giulio