I could be wrong but I don't think they were designed to power camcorders for recording purposes. Could be it has just enough power to charge the battery but not run the camcorder while recording. How long are you recording for? I only ask because it seems as though the camcorder battery does not last long enough. Do you remove the battery from the camcorder when it is not in use?
This is what I could find on the Canon BP-718 battery:
Capacity Minimum: 1790 mAH
Typical: 1840 mAh
Rated Voltage 3.6 VDC