I purchased a used 2017 S90 T5 Momentum in April 2018. My wife was the primary driver of the car. When I drove it I noticed the few times I used the buttons on the keyfob they were not very responsive. It would take two or three presses to unlock a door or open the trunk.
Recently we sold our other car and I have been using the S90 more. The keyfob had gotten worse. It was taking up to ten presses of the keyfob to get a response. Worse yet on several occasions while I was in the car a message appeared indicating the key was not present, when it was in fact in my pocket.
I was thinking of taking it in for service, but decided to try a new battery in the keyfob before I did. Replacing the battery solved all the problems. The buttons now work on the first push and I have received no other error messages.
What is disappointing in all of this is the car never indicated that the keyfob battery needed to be replaced as the owner's manual indicates.