I changed the batteries in a new UX120-018 line voltage data-logger and then found the battery icon disappeared from the display in the upper right-hand corner of the logger and later when connected to a Windows PC via HOBOware Pro version 3.7.23 the battery was reported as "bad". I had installed Energizer Ultimate Lithium Batteries because of their extended 20 year shelf life and they were guaranteed not to leak. The problem I had was caused by how the lithium batteries actually measure 1.8 VDC as compared to the alkaline batteries which measure 1.4 vdc so the logger reported the higher voltage as bad. The fix for this is to go back to regular alkaline batteries. For what it may be worth, I had read in the ONSET literature that lithium batteries were acceptable for use in the logger.