I have heard a lot of people complaining about the battery life of the CR2025 batteries in the MQB Kessy keyfobs. Some have found they can jam in a CR2032 into the space and it works but its not recommended. I recommend getting a good name brand CR2025 battery, you can find them in bulk on amazon.
The real issue here is how much the key communicates with the car and the cars current status. The key is always searching for the car and if it senses the car will try and communicate with it. This connection varies drastically based on many factors such a material of walls, other signals around it and range away from the car.
The range the keyfob communicates is different from the range the keyfob can unlock the car or the range it can unlock the door via handle sensor. The signal needs to be much closer to use the door handle unlock than unlocking on the button on the Kessy remote. The range at which the keyfob can communicate with the car is great than both of these.
Another thing to note is when the car is unlocked the key communicates more than when the car is locked and in sleep mode. One issue I have seen is if you put your car in a garage and leave it unlocked your key will still be trying to make constant connections to the car when in range. Locking the car eventually puts the car in sleep mode and reduces the amount of these connections.
So how to do we fix this? First is always lock the car even when in a secure location. Second is to put the key in a location where it cant communicate with the car. For me, my keyfob can communicate with my car from my couch even though I have a detached garage. Instead I need to put the key in a container that blocks the signals from communicating with the car. A simple metal box is good enough to do this in most situations. You are essentially looking to create a faraday cage. I have it by the door like a key hook or basket some use, I just place the key in it when I come home and take it when I leave.