Zen Mobile — Zen Mobile original Battery became dead within first 8-9 months use

Address:

Panchsheel Nagar, Uttar Pradesh, 245101

I purchased Zen mobile worth Rs 1300 online. It stopped working after 7 months of normal usage. I located and visited Zen Care center. there i was informed that it has some problem internally that was rectified since mobile was in warranty. Also informed me that Battery is also damaged and needs to be replaced. It will cost around 700 Rs since battery comes with a 6 months warranty. Now i am unable to understand how an original battery can go dead in just 7-8 months when usage is even below average. for a 1300 Rs. mobile, does it make sense to spend 700 Rs just for battery. Why every part of the mobile is not with 1 year warranty. Is it just to make fool of the customer?