Super capacitors are new power source, compared to batteries need different charging and power usage.
In previous version I have used 10F 2.7V supercap and step-up converter, it can suck scap voltage up to 0.3V
this solution effectively using energy but but unfortunately consume much more energy than standby RTC.
I have now about 7 days standby life on 1,5F supercapacitor
temperatures RTC, CPU
timer2 in async mode
RTTTL melody player
Alarm 1, configurable time, date, days in week
Alarm 2, configurable minute, hourly beep or time talk
sunset, sunrise time for selected earth position and date
Hi, this can save energy using e-paper display. you only need energy to change the display content and then you saving. For night, it can have really small led light.