Hi,
I would like to power an Arduino ESP32 with an Ion battery, but I noticed all max voltages are 3.7V, and the minimum Arduino ESP32 Vin is 6V. Could I connect two of those batteries in series to power the Arduino?
Yes, that will work.
Follow up question - I would like to charge two Ion batteries using 6V/1.2W solar panels and the Sunny Buddy. Three panels gives enough wattage for one battery. Could I charge two batteries with those three panels or would I need six total?