I'm glad you're enjoying the WildLogger! What you're doing fits exactly the purpose of this course. It's demystifying the art of customizing research equipment. For the WildLogger, if you will be using it to collect scientific grade data, I recommend to upgrade the board to use an external analog reference. There's already a footprint and we will add that to the shop this week. It's a cheap part but will stabilize the ADC reference vs temperature and also has 0.1% accuracy so that you will get more accurate ADC readings across temperature. I think we're targeting $1 for that part so it's a cheap upgrade. Currently the power supply is used as the ADC reference to keep costs down which is accurate to around +/-1.5%.
In regards to the power supply and power requirements, the battery input needs to have a voltage of between 3.6V and 5.0V. A single cell lithium-ion or lithium-ion-polymer battery would be fine at a nominal voltage of 3.6V and full voltage of 4.2V.
in sleep mode with an average SD card that implements power savings modes (like SanDisk), it consumes around 0.8 mA. If you're calculating battery life, you can use that as a theoretical maximum battery life, ie: if you use a 2000 mAHr battery, you would get 2500 hour battery life or ~100 days max. We usually divide by 2 or 3 to get a realistic battery life.
We'll also be making some bonus sensors and training materials specifically for the WildLogger so people can extend it to different applications. We'll announce that soon, likely once we're caught up on the video creation. Also do let us know if you have requests for sensors, displays, etc.
Hope that helps and let me know if you have any other questions.