18650 battery powered Arduino DS18B20 temperature sensor would lost many years without to re-charge or replace the battery, for temperature sensors its best to use 3.3v Arduino Pro Mini with lower clock speed to conserve battery. To optimize further i have removed power LED, and status led connected to Arduino mini pin 13, then feed power to Arduino mini through raw pin with 18650 battery. i have these sensors running over 16 months now and battery is still 96%. It is very low power arduino with DS18B20 temperature sensor.

Pihome 18650 Battery Powered Temperature Sensors

Pihome 18650 Battery Powered Temperature Sensors

Pihome 18650 Battery Powered Temperature Sensors

Pihome 18650 Battery Powered Temperature Sensors

Battery powered DS18B20 1-Wire digital temperature sensor

Battery powered DS18B20 1-Wire digital temperature sensor

DS18B20 with Arduino and nRF24L01

DS18B20 with Arduino and nRF24L01

Battery powered DS18B20 1-Wire digital temperature sensor Schematic

Battery powered DS18B20 1-Wire digital temperature sensor Schematic

Here is MySensors sketch i m using for temperature sensors for low power DS18B20 1-Wire digital temperature sensor node.

For more information about NRF24L01+ connection with Arduino please check this link