RTC battery status

General
1

Two questions for the price of one ... but concatenate

Question 1 :

If I put command

[dmesg | grep rtc]

into an exec node, I can read the output like this :

[ time] rtc-pcf8563 2-0051: low voltage detected, date/time is not reliable.
[ time] rtc-pcf8563 2-0051: registered as rtc0
[ time] rtc-pcf8563 2-0051: low voltage detected, date/time is not reliable.
[ time] rtc-pcf8563 2-0051: hctosys: unable to read the hardware clock

if battery level is NOT GOOD

or

[ time] rtc-pcf8563 2-0051: rtc core: registered rtc-pcf8563 as rtc0
[ time] rtc-pcf8563 2-0051: setting system clock to 2025-09-29 04:15:20 UTC (1759119320)

if battery level is GOOD

There is another system change message when level became low BEFORE fall under critical level, like a warning?

Question 2 :

This message is updated during session?
In other words, if I start system with a correct battery level and I read a GOOD message and during running state the level reach the warning status, another message readable by dmsg will be emitted?

2

Nop, the he PCF8563 has an on-chip voltage-low detector.
There's no option to read the current battery level.

If you get the lowbattery warning you have most likely a couple of months to change the battery. The standby current of the PCF8563 is very low.

3

Thanks a lot.
I'm waiting for the RTC battery to test in real condition.
Your answer means there is an interval between the first "low voltage detected, date/time is not reliable" message and the message "hctosys: unable to read the hardware clock"?
BR