Current fuel cell life expectancy averages between 7 and 9 years.  However, operating conditions and environmental factors can affect the life of the fuel cell.
Some tips for prolonging the life of a fuel cell include:
Avoid exposing the cell to cigarette smoke, both in breath samples and in the ambient environment.
Avoid storing the device in extreme temperatures.
Use the device regularly.  Leaving the instrument in storage can cause the cell to dry out, which reduces its useful life.
Never submerge the instrument in any liquid or introduce liquid of any kind into the breath inlet or fuel cell port.
Avoid repeated use of breath sprays and mouthwashes to simulate positive results when training or demonstrating the device.