Calendar aging is the capacity loss that happens as a battery gets older, even when it is not heavily used. Lithium-ion cells degrade with time, temperature, storage state, and chemistry, so a device can lose runtime before the battery has gone through many charge cycles.
In cyber security, calendar aging matters because battery health affects availability and reliability. Phones, laptops, IoT sensors, backup power units, and embedded systems may shut down, reboot, or fail to report telemetry when a worn battery can no longer hold a charge. That can interrupt logging, lockout controls, and remote monitoring, creating gaps defenders must plan for. Attackers can also benefit from predictable battery wear in unattended devices, since a weak battery can make equipment easier to disable or harder to investigate. For that reason, defenders track battery age, storage conditions, and replacement schedules as part of asset management and resilience planning.