With the adoption of IOT long runtime on battery power is something that is a huge concern. We don’t mind charging our smartphones daily but if we have a dozen IOT devices in our home we would like them to be invisible and just operate for as long as possible without needing attention. Andreas Spiess has done some research using the popular ESP8266 and a variety of batteries. In his test he was sending data to an IOT database every 2 minutes but for many cases you may only need the device to wake and transmit once per hour, this would greatly extend the battery life.