I installed several brand new 2GIG motion sensors this past weekend. Two of them were reporting a low battery on the panel. I took the first one down, removed the battery, tested it (it tested perfectly) and reinstalled. The low battery message went away. Did the same thing for the second one, battery was perfect, reinstalled, but it is still reporting a low battery. Any reason why it might be doing this? Could it be a defective sensor? Anything else I can try?