I believe solar #iot devices should run from #lithiumioncapacitors instead of batteries because they can be recharged endlessly and have a much larger temperature range. These days you can buy a 250F 3.8V lithium ion capacitor for less than 6$. I am selling kits with a 2V 160mA solar panel, a highly efficient solar #energyharvesting board, a breadboard and a 250F LIC on #tindie https://www.tindie.com/products/jaspersikken/solar-harvesting-into-lithium-ion-capacitor/