Apple India — IPhone 6s battery draining

Address: Thane, Maharashtra, 400601

I purchased an iphone 6s last week from mapple which is supposed to be arm of apple in india. The battery has been draining since i brought it. I took it to the service centre the next day. They checked it and restored the factory settings, but the issue still persisted. This was verified by technician and he suggested that the handover the phone to service centre who may need to open it to diagnose the issue and if required they may replace the spare part or replace the phone.
My argument is that i was given the phone that was not quality checked and was defective. Why should i give it to service centre which is not apple owned who would open the device.Instead i need a replacement or money back.