IPad mini 4 battery replacement

Am I being scammed by my local Apple Store? My 5 year old iPad mini 4 battery is dying. I called Apple support who suggested a battery replacement was likely needed. I made an appointment at my local Apple Store who confirmed it was dying, but told me replacement was not possible for any iPad and suggested purchase of a new or refurbished iPad. Online support suggests a battery service at £99 may be possible (which I believe may be a replacement unit from online articles). What’s the truth here please?