Amongst others, the goal of this project was to study the LoRa channel and network, so quite a few nodes were needed. 30 in total. We programed a subset of each to transmit on a different spreading factor, and a few to use ADR.
The requirements were clear: make the nodes as cheap and as low-power as possible.
We ended up with a ~15 euro price tag, and a deep-sleep current of ~7uA.
This translates to about 8-9 months of battery life for transmitting every 5 minutes.
Some years for hourly transmissions. Not bad!
For the more tech-savvy:
-cn3058E LiFePO4 charger
-LoRaMac-node & esp-idf