@donnib A 3.3V Arduino Pro Mini is recommended for battery powering, see https://www.mysensors.org/build/battery for details. For a comparison between rfm69 and nrf24l01+, see https://forum.mysensors.org/topic/3993/nordic-or-hoperf-radio nrf and rfm use roughly the same amount of power, so battery-wise there is no big difference.