I Built Keychain Powerbank

Added: 2026-05-19

[00:00:00]1% on your headphones during a flight with a crying baby sitting right next to you. This situation can be easily avoided if you had a power bank with you. The problem is most power banks are bulky and inconvenient.

[00:00:11]But this one isn't. You can clip it into your keys or simply slip it into your pocket. Despite its small size, it can fully charge your AirPods or boost your iPhone from 0 to 30. I made a bunch of mistakes along the way, but after watching this video, you will be able to design your own power bank with any capacity you want and any shape you want. Let's go.

[00:00:32]Typical power bank weighs half a kilo and when I put it in my pocket, it literally drags my pants down. [music] Money question, what is inside and what we can safely remove to make it smaller?

[00:00:42]90% are batteries. This power bank has 10,000 milliamp hours. That's perfect for scheduled trips, but for quick [music] daily emergency charge, it's way too much. The next component is the so-called BMS/power manager, which steps [music] voltage up and down and protects the battery from overcharge, over discharge, and overheating. For simplicity, let's call it BMS. A typical BMS has three or four plugs, [music] some old USB A, some newer USB C. We can eliminate all of that and replace it with a single modern standard USB [music] C port that supports bidirectional charging. In simple words, it means one USB can handle [music] electricity in and electricity out. All the extra features, displays, flashlight, and so on >> [music] >> can be removed as well. It's really that simple. A battery plus a BMS is all [music] you need to make a power bank.

[00:01:34]So let's look for some BMS online. The cool option I found is the LX LBC 3.1, which is based on IP 3310 module. It's cheap, [music] quite small, supports 3.1 amp charging over 15 watts, which is crazy for its size, has battery protection, and just one USB C. I ended up ordering this one, but it has a couple of drawbacks. More on that later.

[00:01:57]>> Two days later. In the meantime, the LX board already arrived, so it was time to pick a battery. If you watched at least one video from my channel, you know I would [music] be sick if I didn't mention let's reuse a battery from an old vape. I did that here, too, and I burnt my hands and almost give myself homeless badge. I soldered the battery, connected the phone, and it started charging. But, the battery very quickly heated up. At first, I thought the board was damaged, so I ordered another one.

[00:02:26]Two days later. I connected the same battery and burnt the same finger [music] second time.

[00:02:34]Yes, science. Pain maybe isn't the best teacher, but definitely it's effective.

[00:02:38]I quickly realized that LiPo batteries can safely [music] deliver current roughly equal to their capacity, called 1C, so in this case about 0.4 amp, but the board was pulling almost 5 amps.

[00:02:52]That's more than 10 times the safe limit. After cooling my hands in cold water, I kept thinking. I figured out that if I cut the CC pins, charging should fall back to the slow 0.4 amp mode. But, in 2026, that's painfully slow. [music] My next idea was classic 80650 cell. Most of them can easily deliver 20-30 amps, so it seemed like a safe bet. I started building a cardboard and duct tape prototype. It worked, but it was a bit too big.

[00:03:23]Fortunately, they have a smaller cute cousin about half the size with similar electrical performance, 1,200 milliamps >> [music] >> and safe 10 amp current. Perfect pick.

[00:03:34]Let's design a 3D case. I like using Tinkercad because it's free and easy to learn. It's not the best tool for complex projects, but for a case like this, >> [music] >> it's more than enough. I had two goals: keep it as small as possible and feature it with a strong keychain loop. [music] That's my final shape. To be honest, I don't like this square base. Ideally, I need BMS matching the diameter of the cell. I also noticed another drawbacks of the LX board. [music] USB A parts on the bottom that unnecessarily take up space and make the board larger. Also, it uses USB port, [music] a female connector instead of a plug.

[00:04:08]That means I'd have to carry a cable [music] with me all the time. So, the thing I was hoping to avoid has happened.

[00:04:14]I need to design this board from scratch by myself, but thanks to this video sponsor, PCBWay, that's actually possible. They manufacture high-quality PCBs, offer excellent customer support, and super fast worldwide shipping. But, the most important, they provide PCB assembly services, meaning they can solder even the tiniest SMD components for you. Some SMD parts are literally the size of a grain of sand. That saves a huge amount of time and frustration.

[00:04:41]On top of that, they also offer precision 3D printing services, which I already used today to make a custom [music] case for my power bank. They support a bunch of other useful services like CNC machining, that can turn ugly cookie-tin prototypes into clean, professional-looking [music] projects.

[00:04:56]If you are a maker, we prepared $5 coupons to help get you started, so make sure to check out links in the description. Research [music] time. I compared a couple of popular chips from IP53 family and proceed with the same [music] chip, which is super small, like 1/5 of my thumbnail, and supports all features I mentioned before.

[00:05:16]Unfortunately, information about IP family chips is like freaking Atlantis.

[00:05:21]LLMs don't know a damn thing about them, and nobody has ever shared a proper circuit showing how to use one with a USB-C connection.

[00:05:31]The only decent resource I could find was the manufacturer's data sheet. I literally spent over 2 weeks gathering [music] bits and pieces of information, even translating Chinese data sheets. I managed to find one example circuit, but it was designed for USB A. Skipping the details, I removed those parts of the circuit and started putting my own version together. Designing BMS was much harder task than I supposed. For simple signal boards, which I did before, [music] you just connected parts and traces, and that's it. But 3 amp is a hell of a current. For these high power traces, laws of physics starts to [music] jump in. You have to bear in mind thickness of the traces, poor copper areas, and ground planes for heat dissipation, add bunch of additional vias to handle the current. As I said, my first idea was to shrink the board to match the diameter of the battery. So, I removed all the optional components like diodes, the push button, and the thermal fuse, which, by the way, you should never do.

[00:06:25]Sadly, my PCB design sucks, [music] so eventually, after long hours, I had to wave the white flag and make the diameter bigger. The 3D models and PCB design are done. As a plan B, I will order also square model. I just drag and drop the files onto the PCBWay website.

[00:06:41]So, now I have to patiently wait for the package. One week later. Parts arrived.

[00:06:47]Let's start with square version. For 3D print, I picked PETG material, and I can highly recommend it. It's light and super durable.

[00:06:55]It's super straightforward. However, I messed up the box dimensions. I made it about 2 mm too short, so instead of a nice snap fit, I had to save it with hot glue.

[00:07:12]After some final polishing, it doesn't look like a million dollars, but it [music] works. Now, my custom board. It looks weird, but there is only one copy of this board in the world, which is pretty cool, right?

[00:07:24]Right?

[00:07:25]Remember when I mentioned that I wanted a USB plug directly on the board?

[00:07:29]>> [music] >> Well, I messed up again and ordered the exact same port. I guess I'm just doomed [music] to carrying a cable in my pocket. That's the moment of truth. I'd say there is about 70% chance that the board is going to explode when I connect the battery, but let's give it a try.

[00:07:48]Sadly, it doesn't work.

[00:07:54]Okay, I made so many mistakes that I already feel I should start working on version 2.0. Here are the most important things you should avoid if you are making something similar. Remember to add airflow holes or extra heat dissipation surfaces. Always print or order a backup case with [music] a slightly larger dimensions. And last but not least, make sure to properly design your PCB. If you want to see version 2.0, make sure to leave a like and comment. One last disclaimer, if you are planning to build a similar project, be aware that batteries store a lot of energy and if handled improperly, can cause fires or serious injuries. That's it for today. Thanks for watching.

[00:08:33]Subscribe for more and hopefully, see you soon.