My 5 year old AcuRite Weather System outside monitor battery life was only about 5 months long as compared to the first batteries that lasted 5 years, I suspect. Opened up the outside sensor unit and found a moth jammed inside. Not really sure that the moth caused the battery drain but I did remove the moth, replace the batteries and reinstall the unit 20 feet in the air.
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Now in October of 2020 the outside unit batteries are dead again after only 5 months!