Iphone 6s battery replacement issue

Dears, I faced an issue in the apple authorised service centre today and I would like to take an advice from you all on this. I'm using iPhone 6s for the last two years and the phone battery was draining too fast for the last few weeks. After apple announcing battery replacement program i decided to take my phone to apple service center for battery replacement. The consultant at the service center ran diagnostic in my phone and showed me the phone has problem in battery and also in the audio system. And he advised me to change the whole unit instead of battery alone. The battery alone costs about 2250 INR (35.5 USD) and the whole unit costs about 26500 INR (418 USD).

As a user I'm not facing any issues while speaking in phone or while using speaker but the diagnostic tools shows there is problem in audio system as well.

I've decided to take your advice on this. Please help me on this.