Why we live in a sad world where I had to make my own powerbanks
This page: Europe and ICAO Just Screwed Over Many People with 2 Powerbank Limit on Planes explains why people who rely on powerbanks to power things, are now screwed, at least in Europe. Please read that page for more details, but the summary is, they just passed a law earlier in 2026, and I found out the hard way. It boils down to:
- you can still have 2 powerbanks, of any size below 100Wh, but only 2
- so the tiniest little phone booster I have in my pocket (I travel with 4), counts as 1
- I was going to an off the grid festival and had 4 real size powerbanks (90Wh+), so after trying to take off from Wroclaw in Poland, they told me to get rid of 2
- This didn't count the extra 6 smaller 60Wh powerbanks I had to power my LED outfit. Those were not allowed at all either, because too many
- Now, what is a phone but a powerbank with a screen? These are thankfully allowed
- What is a laptop but a powerbank with a screen and keyboard? Those are fine too
- And you can have 20 raw lithium batteries. The ones that are not safe, the ones that will catch fire if you pierce them, and the same one that can cause a fire if you short them, which is easy to do on some.
So there we are, now I have to go back to using raw batteries, even to power USB things like my outfit LEDs, which basically means I need to build powerbanks with raw batteries (which means the batteries get counted as 20 batteries, and not powerbanks, and then I plug in the powerbank module and they become powerbanks after I'm already past airport security)
So now, I'm forced to make my own powerbanks again
I Emailed every powerbank manufacturer I bought from, and let the know they should seriously consider modular powerbanks where the battery can be unplugged and carried separately so it counts as a lithium battery with has a limit of 20, instead of powerbank which has a limit of 2 or 1, or even 0 depending on the country.
A few listened to my feedback, but I'm not sure they took it that seriously, or the fact that their powerbanks are literally getting banned in planes in more and more countries this year.
As part of looking for new batteries, I found foxbuying.com which made custom Li-Ion packs of multiple form factor and voltages and the support person I talked to was amazing in how much they cared and were willing and able to talk tech. As part of that, they gave me recommendations of powerbank ICs to look for on aliexpress, which was very helpful for my search.
Considering if Lipo Batteries would work, the devil I knew
The irony is that I used to use lipos for my LED outfit, mostly because it's what I already had from flying RC planes, but the truth is that they are not the best choice:
their energy density is not actually that great compared to Li-Ion batteries, Lipos are meant for high power discharge, which I don't need on my LED outfit (it uses up to 20W or so), so they are bigger and heavier for no godo reason
lipos are still optimized for weight since they are used in RC planes, so they have little anti fire protections. They can be pierced pretty easily and will catch fire
if you short lipos, you're going to have a bad day, they can put out 100A or even more, enough to melt a lot of things
of course lipo packs need to be carefully balanced or you could overcharge a cell and get it to catch fire
and if you over discharge them, you will damage them forever
plus you need a custom balancing charger to charge them carefully, and those chargers are usually not small
Given all of this, it's kind of a miracle that I used them for more than 5 years without any issues (even if my circuits did have fuses and I was religious about using low voltage alarms).
I didn't have a lot of luck finding nice lipo packs that weren't too big, and I found this one:

6S 88.8Wh
but the issue is that it had no BMS, so I checked if I could find small balancers I could just connect forever, and by the time I got them, I realized they were huge and even their balancing plug is not the same size as the one on batteries.
As part of the BMS boards I found on aliexpress (thanks to foxbuying.com), one of them supported lipos and balancing packs, which would have been great, but sadly it was configured with undocumented micro resistors on the back that I Was not equipped to adjust:

this could have worked if I could have changed the board to 4S since almost all my lipos are 4S

turns out after days of back and forth on aliexpress support, I Was told the boards could be used with straight batteries without the balance connector, but still limited to 3S
Too bad it was not configurable for 4S or 6S as I did get it to output 20V for my laptop
So I gave up on lipos.
Trying Powerbank Boards and Picking Li-ion Batteries
I tested lipos while I was waiting for the foxbuying lithium packs to arrive (I bought 2P/7Ah 3S, or 84Wh, from which I was able to get around 70Wh of real capacity).
This other board I received from aliexpress turned out to be the first winner: it supports 2S to 6S, can charge at 60W and also has a USB-A output which is a win for me since my LED outfit does use USB-A


of course, it can make any USB voltage up to 20V and charge a laptop or a phone
The problem with those boards is the poor documentation and I couldn't get that board to charge my batteries, until I saw this on the back:


needed some help from google

the tiny 2/3/4/5/6 solder traces are just right of the display

and finally got the power to flow the other way

added some shrink wrap to protect it
I did built my LED outfit to support multiple voltages and work from raw batteries or USB-PD from 12 to 20V:


and USB-A for my pants and shirt

I can also use the USB-C as output for other LEDs

While going production, finding the right multi battery cables was hard, so many had insufficient wire gauge that was disclosed nowhere in the product

even this male male connectors melted the inside wire

the outside still works, but 0.1 ohms shows poor and cheap wiring
And then, even the foxbuying batteries were not able to deliver the 8A they were rated for. I don't actually need the 8A, but the anti short protection BMS kicks in very late and allows the battery to overheat and melt its shielding. Here, discharging at 8A, I got 78C on this connecting bar that overheated enough to melt the shield

I'll be honest the battery was warm enough to burn my finger, not good...

and this happened on a partial short that was not enough to trigger the BMS short cutoff, not good

and the short was due to this bad soldering point that failed
The best of aliexpress, poor manufacturing and no quality control
A huge thanks again to foxbuying for the outstanding pre and post sales support, as part of that, they recommended:
Lightweight Board (for LEDs): An SW6208 or IP5328P module (18W-22.5W, 1x USB-C, 2x USB-A, flat display).
Laptop Charging Board (for 65W/100W): A standalone SW6308 / IP5388 buck-boost module
While looking for those, aliexpress also recommended IP2366, there are plenty of options and they are small and efficient, it was just hard to find quality boards that arrived undamaged, and none of them came with a case or box, which is still an ongoing issue for me (I'm not much of a 3d case designer).
Then, these boards finally arrived, and those were china at its best, great features, cheap, and 3 broken out of 4 :

shipped with broken screens

shipped with broken button, support wanted to ship me a new button for me to surface mount solder

pretty when it works
So I got a refund for the broken ones, took one week of arguing with the sales person, bought more, and 3 more were broken:

how is that even possible?

the new version with a bigger screen is nice, this is the only one that worked but good luck putting it in english but the IP2366 chip is cool

I had to use google translate to finally find the menu in chinese

and this other bigger screen one was also broken
Those boards were great until I realized that if I unplug the battery to change it, they will not work or initialize until I plug USB charging power and reset the battery info on the screen (how many cells). OMG, so stupid... It was nice and pretty, but useless if it won't work after a battery change. After sales support did not agree that the board should remember last setting and work after a battery change, sigh...
I tested the one non broken board I got to charge 4 batteries in parallel:

starting at 9.9V

after 10H charging, 317Wh charge to 12.6V for 4 batteries (80Wh per bat)
And that's another board's documentation, positive on the negative point. WTF?

Turning Batteries into Stable 5V, 8A RC plane UBEC with 5.2V output
All this time, I have been using an automotive rated 12V to 5V 10A tobsun step down converter from amazon. Turns out it does work all the way down to 9V, but after that, not as much (and it's big). I had issues with my led panels rebooting in the field under high load and when the batteries were not as full. I bought DC 8-36V to 5V 10A 50W Step Down Converter Voltage Regulator but it turned out to be worse, it claimed to work down to 8V but that was untrue and it was even bigger. Waste of time and effort.
So I asked google gemini for help and it suggested RC BECs, which I didn't consider even though I have plenty. The big plus is I wanted to them output 5.25V to end up with more than 5V at the rPi3a after wire losses, otherwise the rPi would slow down and even reboot. Of course ESCs are designed for exactly that and plenty offered 5.25V output, but few had more than 3A output, until gemini offered this one, an 8-16A UBEC with 5.2V output, yes!

tried it under load at 4A and with poor wiring got 4.85V (more on my microcontroller with better wires)
and the best part is that the ubec is much smaller and lighter, triple win!
Thanks to this Ubec that works all the way down to 6V, I did a test with 2 7A/3S foxbuying packs and I'm now able to get 65Wh per battery pack:


works all the way down to 6V, 130Wh discharge

and 160Wh to recharge in 6H
While the foxbuying batteries are not super sturdy and as safe as powerbanks, I already knew that going back to my own battery packs would be less safe, but I also need to be honest that while they are very compact and light, it's disappointing their melt their thin outer shield while delivering the 8A they are rated for:
In comparison, these packs were clearly built with more safety and path redundancy in mind (there was a better sleeve around them I already peeled off before this picture and much better path for electrons to travel):

I however can't use them as I bought them at an electronics flea market for super cheap and they do not have official Wh markings on them other than what I measured myself while testing them. Their shape is also not pocket friendly. This one I took apart to salvage the individual cells and use them for solar lights ;)
The foxbuying folks did recommend to put my own fuses but I'm using cable doublers, triplers, or quadruplers and I would have to put fuses on each and every branch of these cables, which is a bit too much for now, I might do that later, but I really wish this was part of each battery's BMS, as it should be as adding all the external fuses is splitting cables, more connections, more places that can short, break, or go wrong.
For now, I'm going to hope they won't get damaged during use or travel.
And in the meantime solid state battery powerbanks that do not catch fire if you pierce them: https://heybmx.com/ , are still banned.