A friend once showed me a power bank that was so cool that I had to get one myself. Ended up getting two, and here’s why.

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Removable batteries

Let’s start with the feature that I appreciate the most: removable batteries! The TOMO M4 accepts up to 4 18650 lithium ion battery cells, which are very common nowadays and can be purchased from lots of retailers. You can also mix and match cells and even run the power bank with 1-3 cells in it.

TOMO M4 running on two battery cells.
TOMO M4 running on two battery cells.

If you’re feeling adventurous and you know what you’re doing, you could in theory take an used battery pack from a device that utilises 18650 lithium ion cells, disassemble it completely and use the healthier cells inside power banks like this one. They might not be healthy enough to power bigger devices, such as e-scooters, but they might be just enough to charge your phone. This is something I want to try out eventually with things like old ThinkPad laptop batteries since the risk of burning the whole building down is smaller with those.

I’ve previously bought cheap “10000 mAh” power banks from brands like Xiaomi and have had mixed experiences. Yeah, they usually get the job done, but should the battery die in it, then you’re probably just going to throw the thing away because the battery is not easily replaceable. That’s really wasteful.

With the TOMO M4 it’s a matter of sliding the plastic case open and just replacing the cells, similar to what you’d do for a TV remote with AA batteries. It’s so easy that even your grandma could do it!

I don’t understand why it’s acceptable to enclose consumable items like batteries in devices that are difficult or impossible to open up (the real reason is probably profits, right?). The battery will die at some point, no matter how well you take care of it.

If the rest of the device holds up, then the TOMO M4 could realistically be the last power bank I buy.

The cool factor

Now that we’re done with the most practical aspect, let’s look at the display. Once you power it on, you’ll see the green-lit LCD screen light up. The screen shows the charge level of the individual cells during standby. While charging, you’ll see a nice little animation.

But that’s not the coolest part. If you connect a device to one of the USB ports, it will show the voltage and current that the power bank is outputting. Multiply those two numbers and you can actually see the wattage that a device is pulling.

The display does exhibit ghosting, which is most noticeable during charging.
The display does exhibit ghosting, which is most noticeable during charging.

Not everyone probably appreciates this as much as I do, but I just find it to be really cool.

The downsides

There are some things I’ve noticed about this power bank that are less than ideal.

The charging port is micro-USB, which is not that great in 2023. Out of all the IT gear that I own, this power bank is the only regularly used item that charges via that port. I’d love to see this replaced with USB-C port, just for the sake of uniformity. It’s probably possible to modify this power bank and replace the charging port with an USB-C port, but I have not got around to doing that yet.

The display backlight can be turned off with a single click of the power button. However, if you’re charging a device that is close to being fully charged and starts trickle-charging, the display backlight will turn back on. This is less than ideal in situations where the backlight illumination bothers you, such as during night.

The detailed analysis that I mention in the next paragraph mentioned that this power bank “Can be used as UPS”. I put this to the test with two devices: Raspberry Pi model B+ and a LattePanda V1. The Raspberry Pi struggled a lot and the red power LED flickered constantly, indicating issues with power delivery. The LattePanda V1 booted up and ran nicely for a while, but under a bigger load it threw some errors into kernel logs and eventually locked up completely. On a functional level this power bank can probably act as a UPS, but in practice it did not work out for me. Other factors, such as the USB cable used and/or the lithium ion cells that I used in the power bank, might have also influenced the results of this quick test.

LattePanda V1, powered by the TOMO M4.
LattePanda V1, powered by the TOMO M4.

The technical details, in detail

If you’re interested in all the technical details for this particular power bank, then definitely check out this review on lygte-info.dk. It’s a very detailed overview of the capabilities of this power bank, its behaviour under different circumstances and a bunch of measurements and explanations to back it all up.

I also like the way they phrased the verdict: “I will rate it as acceptable.” Short and concise.

The author also reviews lots of other products and has the reviewing process documented in detail.

Closing thoughts

In general, I’m very happy with this power bank. Although I’d probably not recommend it as an UPS for low-power computers, I’d happily recommend this to someone who needs a simple power bank that they won’t have to throw away after a few years.

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