According to an example, a charge level of a battery is detected with a processing resource communicatively coupled to the battery. In response to detecting a battery at full charge, the current full charge capacity of the battery is recorded, and an error cycle count, a design cycle count, and a full charge capacity at a last calibration are fetched. A maximum allowable battery decay level is calculated based on the error cycle count, the design cycle count, and the full charge capacity at last calibration. In an example, in the event that the current full charge capacity is less than the full charge capacity at the last calibration minus the maximum allowable battery decay level, a battery calibration alert is triggered.