Sensor to monitor refrigerator temp

I put sensors in 2 refrigerators communicating through a Zigbee hub. They will only stay online for 8-10 hours and they go offline. I then have to remove the battery for 20 seconds and reinstall it to get it talking again.

So far I’ve disproved that it’s the metal case of the frig, I’ve tried putting the sensor in a sealed plastic bag to help with humidity, I put the sensor in a plastic bag in a plastic cooler with ice packs and it goes still offline.

I’ve found that the cold is hard on the battery, but they are rated for temps under zero and these sensors are rated for -10c, I’m using them at 38f.

I haven’t seen a sensor with a remote probe, any suggestions?

I use the Sonoff TH 10 with an external temperature sensor. It works with WiFi and is outside the freezer. I cut the cable from the sensor and soldered a piece of ribbon cable in between. This way the door closes perfectly again.