A data recording apparatus, which is capable of acquiring and recording data according to the residual capacity of the battery when the residual capacity is small. A recording operation is carried out such that acquired information data is temporarily written onto the memory and thereafter the information data is transferred to a recording medium to record the information data. The data recording speed of the recording medium is detected. The residual capacity of the battery is detected. The expected driving time period for which the data recording apparatus can be driven is detected, based on the detected residual capacity. The quantity of data recordable on the recording medium is calculated based on the detected data recording speed and the detected expected driving time period. The size of data to be written onto the memory is changed based on the detected recordable quantity of data.