It depends on the age of the sensor. Vernier O2 Gas Sensors manufactured after April 2007 can be refurbished with a new electrochemical cell, whereas sensors manufactured before then cannot. (The newer O2 Gas Sensors can be identified by the recessed calibration button on the side, whereas old-style sensors have a calibration button that sticks out of the top.)
Which Oxygen Gas Sensor (O2-BTA) do I have?

The Vernier O2 Gas Sensor contains an electrochemical cell that has an average lifespan of about six years when stored properly (upright). When new, the O2 Gas Sensor has an output voltage of approximately 3.2 V at ambient levels of O2 gas (20.9%). This output voltage decreases over time but will still give good readings when calibrated. Once the output voltage for ambient O2 gas levels has dropped below 1.8 V (or reads < 12% O2), or the signal is not steady, the sensor is considered “dead.” If you suspect your sensor that is still under warranty (5 years) is dead, contact Vernier for technical support. If it is indeed dead, we will offer a free replacement or refurbishment. If your dead sensor is out of warranty, we can replace the electrochemical cell for a fee (as long as you have the newer model). This refurbished sensor will have a 1-year warranty from the time it was returned you. If you have the older model O2 Gas Sensor (that has a calibration button on the top of the sensor) you will need to buy a new sensor. The electrochemical cell in the older model sensors is sealed and cannot be replaced.

Contact Vernier Technical Support for further questions.

This information is regarding the Oxygen Gas Sensor [O2-BTA]. For information about the the Go Direct Oxygen Gas Sensor [GDX-O2] please see https://www.vernier.com/til/4330