As per the Instructions For Continued Airworthiness, there are no periodic service requirements for the KLN-90B. This unit is manufactured to allow "on condition maintenance". The unit monitors the internal battery and displays a message if the battery is in need of replacement. The typical life of the battery is about 5 years but can vary. Southeast Aerospace evaluates each unit and replaces the battery as needed during maintenance. Not every unit serviced needs a battery replacement at time of service.