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Good afternoon, I have a little problem on my hands with some test units I have recently received. PLCs are very new to me.. and I'm learning quickly, so here is some background. I have five test units which are all identical in their control hardware (and I believe in software as well). The units run a SYSMAC C200HS PLC which feeds into a NT30C-ST141B-E HMI. On boot up, three (3) of the test units display "battery lowered" on the first screen.. then it switches to a "connecting to host" screen and stays there. They never leave the "connecting to host" screen.  I went through both the PLC and HMI on each unit and found the HMI's battery was indeed dead. So I replaced that and the units no longer say "battery lowered" and now only shows the "connecting to host" screen.  What's interesting is that the other two (2) units that did not have battery trouble booted right up and opened the home screen of the HMI and allowed me to program and run the test unit as it should. None of the five (5) units have received any programming work or changes since they ran last.. simply a long period of dormancy during which some of the units' HMI batteries died. So I my question is this.. would letting the battery deplete and then replacing it with a fully charged battery cause issues "connecting to host" and if so, where would I start in my trouble shooting process? I am open and grateful to hear any advice on this topic and input you may have based on my situation. Thank you in advance, Ed