A bit lazy day today, spent on eBay and selling some old junk, getting what was already sold ready for shipment, and playing with the Due central node a little. The node now retrieves the time via NTP and sets its local clock, another step towards telling the time to all nodes that are interested. I did some minor changes of the code, added button and photoresistor to the node, and improved the LED support to make them blink smoothly.
The CR2032 node reported battery dead in the morning. I measured the CR2032 cell and found out that the voltage is perfectly fine. That explains what is going on - it must be the air moisture. Either it condenses on the resistors of the voltage divider, or the cheap chinese paper PCB gets soaked and its resistence decreases. I know it's a really cheap PCB and I am not blaming anyone, I bought a pack of fifty for few euros and they so far performed well. Anyway, I'll leave one of them on balcony for a day and see if it will show any measurable resistence.
If the problem is in the air moisture condensing on the resistors of the voltage divider (they're something like 1M5 and 330K if I recall the values correctly), I'll use standard through-hole resistors for the divider, and maybe smaller values. It should not be a problem, I am grounding the lower end of the divider before measurement, thus it should not draw any noticeable current anyway.
Speaking of power consumption - after the node dried up and the reported voltage stabilised at 2920mV, it didn't change a single bit. Did I finally succeed in creating a sensor node that will run off the CR2032 cell for a few months at least? *evil grin*