It may be that the ambient temperature is low, iPad charging needs to be at a constant temperature, less than a few degrees below zero can not be charged, it is recommended to put the iPad in the bed to charge. It is not necessary to discharge 100% before charging. Apple lithium-ion batteries work in charge cycle mode.
1: If the amount of electricity used (discharged) reaches 100% of the battery capacity, a charging cycle is completed, but not necessarily through a single charge.
2: For example, you might use 75% of your battery during the day and then charge your device fully during the night. If 25% of the electricity is used the next day, the total discharge will reach 100%, thus completing a charging cycle in two days. It may also take several days to complete a charging cycle.