def get_ccap(self, cycle=None, dataset_number=None):
        """Returns charge_capacity (in mAh/g), and voltage."""

        #  TODO: should return a DataFrame as default
        #  but remark that we then have to update e.g. batch_helpers.py

        dataset_number = self._validate_dataset_number(dataset_number)
        if dataset_number is None:
            self._report_empty_dataset()
            return
        cc, v = self._get_cap(cycle, dataset_number, "charge")
        return cc, v
Returns charge_capacity (in mAh/g), and voltage.