Measuring power usage over time? What kit is that?

Thanks for the ideas and discussion. I am certainly no electronics engineer but it gives me an idea.

Maybe I could just find the smallest LIPO possible (like this 20mah, retired) and see how long before it gives up.

Neither appreciating, nor understanding how the different battery types discharge, I could at least compare LIPO to LIPO, and as a bonus I could stick it in the freezer to see how it copes in low temperatures. I'd be opening and closing the fridge door every hour to check it.

I say this mindful that if I am going to get serious about this iot stuff, an Oscilloscope will be the right way to go.