These are excellent headphones with great sound and fantastic battery life. As advertised it does last around 24 hr and has a stand by of 21 days which is very good. It also offers deep sleep hibernation upto 180 days. It is very comfortable and can use for long hours. It does support Bluetooth range upto 100 meters for class 1 supporting devices. Active noise cancellation is also decent enough for the price and does provides great performance in flights and noisy surrounding. 3.5mm jack is also provided in case you run out of battery.
You will find it at Amazon, Flipkart and Paytm for around 10k but in Paytm you can get cash-back up-to 3k which will get down the price for around 7.5k. I have personally purchased from Paytm and you can get the offer using the above link.