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The issue is with the temperature sensor board...it wears out over time. It will drain batteries in a few days. Fortunately, Acurite sells a replacement board “'''AcuRite Iris (5-in-1) Temperature and Humidity Sensor Replacement”''' it is a cheap fix ~$13 + shipping. I changed my board out about 2 years ago and it's been working fine.
Here's a link to order the part from Acurite:
https://www.acurite.com/shop-all/weather-instruments/weather-sensors-and-parts/sensors/temperature-and-humidity-sensor-replacement-for-5-in-1-weather-sensors.html?ref=name
They will include the documentation on how to replace the board - it's a phillips screwdriver to open the sensor and the board simply unplugs.
I've had to replace a couple parts on the sensor - the top fan also stopped working, this makes the temperature read higher than what it actually is.
Overall, I've put $40 in replacement parts into the outdoor sensor, and I expect to get at least a few more years from it (the full replacement sensor is ~$100).
I have to give Acurite some props, they really make the sensor VERY repairable.