Unit displays Battery Calibration requuired

Step1. Have the battery been fully charged. 
Step2. Remove the battery from the ventilator for 2 hours. The battery will calibrate the voltage of fully charged itself during these 2 hours. 
Step3. Put the battery back to the ventilator and have the battery been fully drained. (Use battery only till the ventilator is turned off automatically.) 
Step4. Remove the battery from the ventilator for 3 hours The battery will calibrate the voltage of fully drained itself during these 3 hours. 
Step5. After 3 hours, recharge the battery to 50%. Then the alarm should disappear. Step6. The battery could be used as normal after the calibration.