Shipments of DL units between June 27 2014 and August 1, 2014 (Firmware feature version 27) had a firmware problem where battery-powered power-save-mode readings may have been missed.
A new version (feature 29) correcting that issue is available here:
http://unihedron.com/projects/darksky/cd/SQM-LU-DL/firmware/SQM-LU-DL-4-6-29.hexUnits with the older version 25 firmware do not need to be updated, the bug does not exist in that version.
Sorry for the inconvenience.