Had this happened to me. I ended up changing the battery for both key fobs then driving in the vehicle with both fobs. This finally stopped the low battery warning.
I had driven with either key inside the vehicle and constantly got the warning.
It seems like the batteries in the fobs go out quite early. I picked up a 2024 start of the year and the fob had a dead battery. I have fobs I have been using for 15 years and haven't had to change the batteries. Must be a lot of activity happening in the fob I am not aware of.
I believe the keys go to sleep after a few days as long as it's not within range of the vehicle and as long as the key isn't physically moved (based on an internal accelerometer).
If it's at least 6 feet from the car (preferably through a wall) and the key isn't periodically jiggled, the battery should last considerably longer.