The problem is finding the atom lite schematic. It is not clear what voltage stabilizer was used. I suspect it has a voltage drop between input and output of ~1.0-1.2V. I connected a li-po cell (4.2V 900mAh) directly into the 5V input. I measured the cell voltage and sent the data to the local blynk server every 20 seconds. Additionally, I measured the internal temperature of the esp32 chip and it oscillated at a constant 50-51°C. With this connection the chip worked for about 6.5 hours and then turned off or stopped working properly at 3.41±0.1V cell voltage. So the esp32 chip probably stopped working at ~2.2-2.4V on a 3.3V supply line. I don't know how usb-uart converter will work with supply voltage lower than 5V. A colleague from "Esp Poland" forum tested power supply for ws2812 diode and at 3.9V the diode went crazy. Screenshot from blynk contain: cell coltage esp32 internalge temperature atom lite uptime/working time