At some point all Air Scale sensors will need a new battery, and it's easy to change them.
Most of you will have the newer model sensors with the metal base. If you do have the old model sensors that are all plastic, you can find better instructions for them in this video.
First, unscrew the cap of the Air Scale sensor. If your sensor is not installed on its t-fitting, then you may need a wrench to hold the metal base to loosen the cap.
The battery is held securely in place by a bracket and blocked on one side by the Bluetooth antenna. You may need to use something smaller than your finger to push the battery out of the bracket without bending the antenna.
The battery you need is a 3 volt lithium battery model CR1632. You can find them at most big box and automotive stores.
Be careful of the Bluetooth antenna when sliding in the new battery. Stop when you feel resistance.