This esp32 tutorial can teach you how to make a fruit battery and it verifies the low power consumption of the FireBeetle Board-ESP32. 

Verification for Low Power Consumption of Firebeetle Board-ESP32

Modify the program to let the ESP32 chip to immediately enter deep sleep at low power consumption after power-on. The sleep lasts for 2 minutes. Restart the chip 2 minutes later. 

Connect the negative pole of lithium battery to GND of FireBeetle Board-ESP32 main board, positive pole of lithium battery to positive pole of digital multimeter, negative pole of digital multimeter to the positive pole of FireBeetle Board-ESP32. The lithium battery supplies power to FireBeetle Board-ESP32 through the digital multimeter.

Current tested: 11.897uA.

Conclusion: The current of the whole module is about 10 uA when FireBeetle Board-ESP32 main board enters low power consumption.

Power Supplied by Fruit Battery

The fruit battery is made of lemons, copper plates and galvanized iron nails. The copper plate serves as the positive pole and the iron nail serves as the negative pole to replace the original lithium battery for power supply (ESP32 cannot be driven by the fruit battery when started due to large current, so it shall be driven by the lithium battery. After ESP32 is started, replace the lithium battery with the fruit battery for power supply). 

[Materials preparation]

▲FireBeetle ESP32 IOT Microcontroller (Supports Wi-Fi & Bluetooth)

▲Wires x4

▲Lemon

[Building of fruit battery]

Electric quantity of single fruit battery cell:

The electric quantity tested of single fruit battery cell is about 1.16V, so the electric quantity of four fruit battery cells is about 4.5V:

Current tested: 9.514uA

 
The power supply consumption of fruit battery is: 9.514uA (about 10 uA).

DFRobot supply lots of esp32 arduino tutorials  and esp32 projects for makers to learn.