CR2032 battery discharge pattern

The Funky v1 + DS18B20 room temperature monitoring project that I installed in our living room on October 31st 2012 has stopped sending. This actually happened few days ago (Aug 10th 2013), but I just noticed it today while checking the graphs. That makes 9 months and 10 days of run time on 220 mAh battery, sending the room temperature measurements every 5 minutes (no ACKs). Pretty good given that the code wasn’t optimal as I discovered ways to work with the DS18B20 in a more efficient way later, plus I could have used reduced transmission power as the living room is really close to the gateway. With the new code, it should last much longer, probably couple years on Funky v1. The project runs on a CR2032 coin cell battery and reports room temperature in degrees C and battery voltage in mV:

cr2032

The above chart is generated using pChart as per my post here.

I am really puzzled with the battery reading, especially the sudden drop to 2.8V few days after the project started. It slightly recovers afterwards. The connection between room temperature and battery voltage is also obvious. We were on a vacation around Jan 10 2013 and the house wasn’t heated, hence the sudden drop in temperature. The battery level also dropped notably.

Anyway, this project provides knowledge of the expected discharge pattern for the CR2032 coin cell battery.

 

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