I recently finished the prototype for a battery powered ESP8266 based temperature and humidity sensor with eInk display. Currently working on a custom PCB. : r/arduino
IoT-Based Battery Status Monitoring System Using ESP8266
Tom Horton | DiY IoT | Building a Battery-operated ESP8266 Sensor Module
One ESP8266, One Battery, One Year… And Counting. | Hackaday
Amazon.com: for WeMos D1 Mini ESP8266 WiFi Module with Battery Slot ESP-Wroom-02 Motherboard 18650 Charging Battery Development Board Compatible with NodeMCU : Electronics
Amazon.com: OCESTORE Mini D1 Module Wemos D1 ESP8266 with Battery Slot ESP WROOM 02 Motherboard Compatible with Node-MCU : Electronics
Adventures in deep sleep with ESP8266 and a temperature sensor – Tomás McGuinness
GitHub - tzapu/DeepSleepDHT22: Battery Powered ESP8266 WiFi Temperature and Humidity Logger