Tata Motors — tata nexon xz+ car key cell problem

Address:

Ahmednagar, Maharashtra, 422605

Resp. Sir, my car number is mh17 bx 2631. This is to reveal that since last eight months i am using nexon xz+. I have complained about the key to nearest delear at nasik/rahata regarding it's cells. I came to know that the cells are not available in delears inventory.
I had to purchase the cells in local market but are not durable. First of all i don't know that how can a cell discharge within four months of purchase of car?
Secondly when i tired to open the door manually it opens but the siren starts as if theft alarm. Is there any remedy to start a car manually when the key cells get discharged? Otherwise there is no use of this expensive car in case of emergency.
Yesterday night only i faced this problem. Is it not a flaw in this high tech car? please help me out to solve this problem.