Average fuel cell life is 7 to 9 years, depending on use. As a fuel cell ages, it begins to take longer for the sensor to produce the information needed to calculate the result. The slowness of the cell does not mean it cannot produce consistent and accurate results. However, if the speed to result is an issue for the user, the slow response of an older cell could be a limiting factor that determines when to change the cell.  The best indicator for a user to determine if a sensor requires replacement is if it will not consistently maintain calibration. This is not to say that a sensor that goes out of calibration once should be replaced, but if an instrument proves to be unable to maintain its calibration over long periods of time (months, or even years), the unit should be inspected by a technician. In order to reduce the likelihood that an instrument ever has a fuel cell that goes bad in the field, Intoximeters offers a preventative maintenance program called a "Recertification". Click on the link below to learn about this program.