MoodleBox without AC: it works beautifully!

Germán Valero

MI just tried to use my MoodleBox (Raspberry pi 5) with a powerbank for a cell phone.
I got a very powerful powerbak for a telephone with a 65 watts output and the right connector for my MoodleBox.
I have been using it for half an hour and it still has 91% charge available.
This is a very good finding.
The power bank rated 65 watts output is a lot more than the 45 watts of the Canakit power supply; it is ,most likely an overkill.
The cost was about 50 US dollars in a store for cell phone goodies. It would probably be less expensive if bought online.

DETAILS:
System information
Free space on SD card 106.2 GB (91%)
CPU load 0.055, 0.068, 0.139
CPU temperature 61.7 °C
CPU frequency 2400 MHz
System uptime 48 mins 48 secs
Hardware information
Raspberry Pi model Raspberry Pi 5 (8GB RAM)
Model revision 1.0
Model revision code d04170
Software versions
Raspberry Pi OS version Debian GNU/Linux 13 (trixie)
Kernel version Linux 6.12.62+rpt-rpi-2712 aarch64
MoodleBox version 4.11.1 (2026-02-15)
MoodleBox plugin version 3.2.0 (2026040301)
Moodle version 5.2+ (Build: 20260501)

Germán Valero

96% remaining battery after 48 minutes uptime !
This is great!

Thanks to Ralf and Nicolas for this great MoodleBox.

Ralf Krause

I have a powerbank which can be used with a laptop. This works fine with the Raspberry Pi 4B and 5. I bought an usb tester to see the electric parameters voltage and current. It's looking fine … 5.15v and 0.824A while I am connected with an iPad and opening a course. The current test runs since 14:43 … since nearly 8 hours. I will how long it takes until the powerbank is empty.

Ralf Krause

Now, I wanted to find out exactly how long the MoodleBox lasted on a single charge. I had assumed it would be quite simple to locate the relevant entries within the Raspberry Pi OS log files. However, it appears these logs are stored in volatile memory—presumably to minimize wear and tear on the microSD card.

Fortunately, Moodle stores the results of its scheduled tasks within its own database. And I was able to find the exact start of my experiment. I launched the experiment—and snapped the photo of the USB tester—on May 12, 2026, at 14:43. It is at this precise moment that I find a gap in the task log data. After all, I had just unplugged the power adapter and switched to using the power bank instead ... a transition that caused the MoodleBox to reboot.

In the next step I needed to locate the next gap in the task logs to determine exactly when logging ceased—indicating that the power supply had finally failed. The very last entry—bearing PID 12857—was recorded at 05:48 on May 13, 2026. Then, at 06:28, the first entry following a system restart was recorded, this time with PID 1343. The PID (Process ID) sequence resets whenever the Raspberry Pi reboots, encompassing all active system processes. Consequently, any processes sharing the same PID within the task logs were likely triggered by the same underlying cron job.

For me, this proved to be an instructive experiment. I learned how to identify operational interruptions within Moodle—even in the absence of corresponding operating system log data. Furthermore, I now know that my MoodleBox, powered by a laptop-grade power bank, managed to run for just 15 hours. During this period, I had two devices connected to both the "MoodleBox" WiFi network and the Internet.

Armed with the insights gained from this experiment, it would be a simple matter to determine just how much additional power the MoodleBox consumes when an entire class of students is accessing it and actively engaging with a Moodle course. Another indicator for such an experiment can, of course, be the percentage display on the power bank; however, even for this, you must first test whether the MoodleBox continues to run when the display drops below 5%, below 3%, or even to 1%.

Best regards,
Ralf

Nicolas

Thanks for these experiments regarding MoodleBox running time with a powerbank.

However, an important thing to take in account in the context of using powerbanks with MoodleBox is whether undervoltage situations occur, especially when an entire class of students is accessing it and actively engaging with a Moodle course (as writes Ralf).

We already talked about this in these forums, and what I wrote then is still correct.

For context: undervoltage situations leads to stability issues, notably with the wireless network connection of client devices. These should absolutely be avoided.

@Germán Valero @Ralf Krause Did you experiment undervoltage issues in this context?

Germán Valero

Hi Nicolas.

I used the powerbank for making the server upgrade to 5.2, while I had only one PC accesing the MoodleBox via Wifi.

My semester will end by June.

I may have some holidays later, but I am engaged to be married soon, and I do not know if I will have enough time to do some tests with real students accessing the MoodleBox soon. If I do, I will write my findings here.

In the meantime, I want to thank you and Ralph vehemently for the great support for the great MoodleBox.

Germán Valero

Not being an engineer, I would guess that my powerbank rated output of 65 Watts is far greater than the 45 Watts the kanakit AC adapter supplies.

Therfore, I do not think an undervoltage situation is likely to happen even when the server is doing very demanding work; at least not for many, many hours.

But a proof of concept merits some experimenting.

These are the best of times (for using a MoodleBox).

Ralf Krause

Hi Nicolas,
yes, I tried to get the undervoltage message on the screen. I took my old Powerbank 20000 mAh. This Powerbank has two ports for USB-A. The first one has 5V/1A and the second one has 5V/2A. I connected a Raspberry Pi 4B (4GB) with the MoodleBox 4.11.1, upgraded to Moodle 5.2 (the upgrade test for German).

It seems to be no problem with the Raspberry Pi 4B. The usb tester shows 4.96V and mostly less than 0.5A. There are two connected devices. I did the update of the MoodleBox 3.2.0 plugin and the current got 0.8A. The next test was purging the caches. For a moment the voltage got 4.83V and the current 0.97A. With the Raspberry Pi 4B and Raspberry Pi OS (Trixie) I got no undervoltage message with the old powerbank.

Yes, I remember that I got this message with the Raspberry Pi 3B+ and an older Smartphone power supply. But currently I got no message with the powerbank. I will see how long it takes until the MoodleBox stops.

Ralf

Ralf Krause

The test using the Raspberry Pi 4B began on May 13, 2026, at 18:12 and concluded on May 14, 2026, at 10:45. This means that the Raspberry Pi 4B—powered by the old power bank, which supplied a voltage between 4.8 and 4.95 volts—ran for a total of 16 hours and 33 minutes. To get these data I inspected the task log data in the same way as I described yesterday.

During this time, two devices were connected to the MoodleBox Wi-Fi and were actively in use. Using one of these devices, I accessed and read various websites until approximately 22:00.

Furthermore, I performed a MoodleBox update from Moodle 5.2+ (20260501) to 5.2+ (20260512), updated the existing language packs, and installed two additional language packs: de_du and de_kids. I got no message for undervoltage.

I consider an operating time of over 16 hours on a single power bank to be sufficient to last through a full school day—even taking into account that the MoodleBox would consume more electrical energy if connected to 20 devices.

Best regards,
Ralf