We chose 3.7V lithium cells instead of standard batteries (such as alkaline or 9V) because the ESP32 requires high current peaks for Wi-Fi communication, which conventional batteries cannot reliably support.
We opted for the cylindrical 18650 format over flat Li-Po batteries due to its excellent cost-to-capacity ratio, offering roughly double the capacity for a reasonable increase in price. Additionally, their rigid metal casing provides greater protection against mechanical damage inside our enclosure, making them a safer and more robust choice for our system.