In order to get detailed information about the subsidy and its eligibility criteria, we would suggest you exchange your words with an authorized dealership or nearest RTO. As these rules may differ in different states. Check out [dealership@click here details.
We'd suggest you please connect with the nearest authorized service center to get exact details regarding the prices and availability of spare parts. Click on the given link and select your desired city for service centers.
It would be unfair to give a verdict here as the battery life would depend on certain factors such as driving conditions, charging cycle, timely maintenance, etc.