I keep my key in a faraday pouch, just over a year of owning my current 8.5 and it’s not required a new battery. As mentioned above, it’s the range signal thing ‘talking’ to the car that kills the key battery, the faraday pouch stops that happening, especially if your key is kept in range between drives. My previous mk8 needed a key battery twice in quick succession until I realised the key was being woken up by my hall table moving as I walked past it, this made the key talk to the car, which also made the coming home lights on the car activate, all of this stopped by using a faraday pouch.