# RTC battery status
**URL:** https://discourse.nodered.org/t/rtc-battery-status/99235
**Category:** General
**Created:** [2 October 2025 08:43 UTC](https://discourse.nodered.org/t/rtc-battery-status/99235 "2025-10-02T08:43:08Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Geppy57](https://discourse.nodered.org/u/Geppy57)
#### Post date: [2 October 2025 08:43 UTC](https://discourse.nodered.org/t/rtc-battery-status/99235/1 "2025-10-02T08:43:08Z")
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?
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### Author:  [@edje11](https://discourse.nodered.org/u/edje11)
#### Post date: [2 October 2025 09:12 UTC](https://discourse.nodered.org/t/rtc-battery-status/99235/2 "2025-10-02T09:12:41Z")
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.
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### Author:  [@Geppy57](https://discourse.nodered.org/u/Geppy57)
#### Post date: [2 October 2025 09:46 UTC](https://discourse.nodered.org/t/rtc-battery-status/99235/3 "2025-10-02T09:46:36Z")
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
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### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [31 December 2025 09:46 UTC](https://discourse.nodered.org/t/rtc-battery-status/99235/4 "2025-12-31T09:46:53Z")
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