I also ordered ml2032,but they take 2months of shipment.the holder/cable should arrive next week so i need a solution to use what i have…and if i can use simple 1n4148 with cr2032 the i can test earlier
And sorry about my fixed 0.7v voltage drop by diode…seems this is burned in my mind 
The clock is powered by the 3.3V from the board, so why do you need a battery for testing? One would think…
But when the i2c communication is started, current draw of the RTC is almost 1mA, a lot more then without i2c.
The voltage drop over the 2k2 resitor would then be 2V, down to 1.3V. But we need at least 1.8V for i2c communication.
This indeed does not make much sense, and we can only read the clock when there is a battery installed?
Just use without diode for testing, I do not think you will immedeately burn your house down. You would be present anyway. But just to be on the safe side, remove the battery after testing, as it is not following the battery manufacturer specifications.
@riskable also seems to have survived the experience. Appropriate nickname here 
In my previous tests i get an error from rtc when it is probed…but yes,maybe i only need to save the clock first and then do only software reboots for testing if the clock survives this…but after poweroff the clock will be reset of course. I always poweroff the boards when not working on them. But problem is on poweron that battery may get hot because it is charged…adding the diode may prevent this and battery damage
I think the voltage drop too low behind R75, if there is no battery…
Hi, thanks for sharing your wisdom, can you help me with this question, can these RTC batteries for Raspberry Pi 5 be placed on the BPI-R4? The 2-pin JST connector is a bit longer, but I think the pitch connector is still 1.25mm.
Or is it better to buy the one you recommend?
It is not up to me to recommend the type of batteries, but up to the manufacturer.
I was only concerned about a possibly dangerous situation, using non-chargable batteries on a charger.
For this reason?
You can use the ML2032 in any device which accepts CR2032, but you CAN’T use the CR2032 in devices which accept the ML2032, because the CR2032, being non-rechargeable, might EXPLODE when trying to be recharged.
Source:
at least i tried if rtc will survive reboot without battery…and it does 
root@bpi-r4-v11:~
# dmesg | grep rtc
[ 1.479923] rtc-pcf8563 2-0051: low voltage detected, date/time is not relia.
[ 1.487390] rtc-pcf8563 2-0051: registered as rtc0
[ 1.493378] rtc-pcf8563 2-0051: low voltage detected, date/time is not relia.
[ 1.500771] rtc-pcf8563 2-0051: hctosys: unable to read the hardware clock
root@bpi-r4-v11:~
# date -s "2024-04-27 09:55 CEST"
Sat Apr 27 07:55:00 UTC 2024
root@bpi-r4-v11:~
# hwclock -w
root@bpi-r4-v11:~
# hwclock -r
2024-04-27 07:56:23.979830+00:00
root@bpi-r4-v11:~
# reboot
...
root@bpi-r4-v11:~
# dmesg | grep rtc
[ 1.480067] rtc-pcf8563 2-0051: registered as rtc0
[ 1.486061] rtc-pcf8563 2-0051: setting system clock to 2024-04-27T07:56:53 )
root@bpi-r4-v11:~
# date
Sat Apr 27 08:00:46 UTC 2024
root@bpi-r4-v11:~
oh, and it looks like it survives ~2h with full power loss (only uart connected but this has no vcc).
As expected from my rusty circuit analysis.
Thanks for verifying for us w/o R4 yet
The 47uF capacitor at VCC_RTC is the hero (thanks to BPI for putting it there). From my back of the envelope calculation, enough electricity to power the RTC for 4-5 hours if not longer when main DC power is off.
To R4 owners:
for all intents and purposes, you don’t need a RTC battery like I said before.
had it off for ~7h…still working…
[ 1.486064] rtc-pcf8563 2-0051: setting system clock to 2024-04-27T11:22:02 UTC (1714216922)
[ 1.486000] rtc-pcf8563 2-0051: setting system clock to 2024-04-27T18:42:44 UTC (1714243364)
today my cables and cr2032 holders arrived
I helped an OpenWrt user to enable the RTC in snapshot for BPI R4. And enabled the RTC for myself as a byproduct. So took the chance to test how long the RTC can survive offline without a battery.
My BPI R4 is 4 hours. RTC keeps the time perfectly fine.
At 4.5 hours, low voltage detected.
@frank-w I wonder how yours lasted so loooooong…
Maybe you have more client-devices which taking current…maybe there is a current backflow over serial-uart…i saw the power led is dimmed when uart is connected…possibly i had not cut off all connections (also using a switchable dc-connector).
Just to make sure…you did start counting from 0 hrs after each round of power off & on and checking the kernel dmesg output?
I have UART (serial debug console) disconnected. Have two RJ45 plugged in. DC12V plugged in but powered off.
Maybe I should try with the two RJ45s unplugged…
Of course started from 0 after poweroff and swited off on my dc powercable…but i guess my serial adapter gives enough power to the rtc
Tested with all RJ45 unplugged. Cannot survive 5 hours.
So I think I reached my conclusion. My R4 and possibly production batch 3 & onwards can survive 4hrs+ but not passing 4.5 hrs.
Still very good.
Guys, need some help. I’m trying to play with RTC, but :
root@munich:~# cat /etc/modules.d/rtc-pcf8563
rtc-pcf8563
root@munich:~# hwclock
hwclock: can't open '/dev/misc/rtc': No such file or directory
root@munich:~#
root@munich:~# dmesg | grep rtc
[ 5.746191] FIT: flat_dt sub-image 0x0058a000..0x0058a11c "fdt-mt7988a-bananapi-bpi-r4-rtc" (ARM64 OpenWrt bananapi_bpi-r4 device tree overlay mt7988a-bananapi-bpi-r4-rtc)
root@munich:~# i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- 51 -- -- -- -- -- UU -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: UU -- -- -- -- -- -- --
Enable RTC on Banana Pi BPI-R4:
Source:
Adding my 5 cents here, task was to get RTC running. Only for those who are able to do fine soldering on the PCB.
From a previous project I had some coin batteries with fixed cables and at the end the little white plug as shown above. I cut one of the cables from one battery and plugged it into RTC connector on PCB of BPi-R4. Surprisingly there was no voltage at the end of the leads. Likely the width of the contacts in my white plug is wider than the size of the pins in the RTC connector. So I added a 2.5 mil 2pin header at the back of the RTC connector. and the appropriate plug on other side. As dicussed above, safety issues to maintain CE, I used a diode 1N4148 and a 2k2 1% resistor, rebuilding the circuitry from the 3.3VD in schematic to supply the RTC from power supply. As the pin header is a pretty good post, I added the elements on the post and soldered the leads of the battery at the other end.
Result: power to RTC can come either from 3.3VD or from coin battery. Tests showed that RTC is now correctly surviving power off even for longer time. As the RTC header is at the supply voltage of RTC chip, I could use it to do some measurement. It turns out that when applying a power supply, the voltage at the post is little higher than when running on battery. This is good as we do not want unneeded discharge of the battery. The diode prohibits voltage going back or even charging battery. The resistor somewhat limits maximum current at battery, so prohibiting heat by fast discharge. Both elements together add to safety.
At the post, so at RTC supply, I measured some 3.1 V which is pretty enough to run the RTC. On initial setup, just with pin header, I measured voltage in original state, the capacitor 47 uF runs out pretty fast, it holds for some minute or two to go below 1 V, which is minimum for the RTC chip according data sheet. So the RTC survives on capacitor a quick power reset, but 30 mins or even less will result in voltage loss VL bit set.
For entertainment, some photographs (of the first prototype) follow to show the basic principle:
Hello,
I have a question regarding replacing the battery for the real-time clock (RTC) in devices. I’m considering using a supercapacitor instead of the standard ML1220 coin cell. Is this a viable option, and what potential issues could arise?
I know that supercapacitors (ionistor) can maintain voltage for extended periods, but they have different characteristics compared to lithium coin cells. Could this affect the proper functioning of the RTC or other components?
I would appreciate any advice or experience regarding the use of supercapacitors in such applications!
Thank you!
