Actually, I failed to say that I first replaced the batteries shipped with another set of alkalines (different brand) and had basically the same results. Seeing that the batteries are the only variable changed, I have to assume the lithiums made the difference. Oh, and by the way, the outside antenna for the WMR100 was about 10 feet from the UV sensor and still was not communicating at night until I changed batteries. When the sun warmed up the sensor all was fine with alkalines, but after dark things went sour.