DIY USB Power Bank

USB power banks give your phone some extra juice on the go. You can find them in all shapes and sizes from various retailers, but why not build your own?

[Kim] has a walkthrough on how to do just that. This DIY USB Power Bank packs 18650 battery cells and a power management board into a 3D printed case. The four cells provide 16,000 mAh, which should give you a few charges. The end product looks pretty good, and comes in a bit cheaper than buying a power bank of similar capacity.

The power management hardware being used here appears to be a generic part used in many power bank designs. It performs the necessary voltage conversions and manages charge and discharge to avoid damaging the cells. A small display shows the state of the battery pack.

You might prefer to buy a power bank off the shelf, but this design could be perfect solution for adding batteries to other projects. With a few cells and this management board, you have a stable 5 V output with USB charging. The 2.1 A output should be enough to power most boards, including Raspberry Pis. While we’ve seen other DIY Raspberry Pi power banks in the past, this board gets the job done for $3.


47 thoughts on “DIY USB Power Bank

  1. When I read “DIY power bank”, I expected his own design of PCB for the power bank. It’s more of a “self printed battery/PCB holder” project really — not that there’s anything wrong with that.

    1. I completely agree here.
      -Also those cells look exactly like UltraFire Cells, which are famous for NOT being the capacity listed, and NOT having working protection circuits (if there is one at all) Real capacity would be at most 2600 ma per cell so 10400 ma if they are decent cells top of the line cells top out at 3200 so 12800 ma. and ultrafire cells top out at around 1000 ma per cell so 4000 each NOT 16000.

      Now I have used a bunch of the $1 single cell packs with used laptop cells, and they are around 72%, but they do not do 1A, 600 ma at the most is the highest output.

  2. Batteries cost kills this project. Assuming you have a 3D printer, batteries for a 16000mah bank and controller is $54. I got a 20000mah bank at walmart for $27, and I can charge 2 devices at once.

    1. Actually, it seems the 4 18650 cells (w/ protection circuit) cost only 12.99 USD, and the controller is only 2.62 USD. Not counting shipping, the total is only 15.61 USD. (Of course, the rated capacity of 4000 mAh per cell is a little optimistic: “…Capacity : 4000mah (tested by the manufacture maybe can not reach 4000mah)…” So, the pack probably isn’t 16000 mAh, but it’s certainly not $54.

      1. Genuine decent cells with real rated capacity are $10 – $14 each.

        The cheap cells are fake, rejects, or mis-labelled with the wrong capacity. Considering their ability to spontaneously combust when mishandled that’s not something I want to risk.

        1. I’m building a new battery pack for my electric skateboard and I bought 50 pcs of Samsung 18650 INR18650-35E cells, with 3450 mAh (I verified this) and max discharge current of 10A for 3.11 € each. These cells were bought from, which is a good supplier of brand name Li-Ion cells in europe.

      1. i had great luck with removal of 18650’s from a 12-cell toshiba laptop battery. the battery was new-in-package, unused, 3 years old, had matching + high quality cells, and then a vape battery charger charged them well. fear of shorting was a concern, but i took my time (½ hour) to do the job right.

        [for anyone disassembling: do it outdoors or be able to throw a burning mess out a window or door.]

  3. I can see at least one good reason for doing this; LONGEVITY! I am currently the (not so) proud owner of about 9 10000mAh external charge packs. They all work great for about a month before capacity rolls off steeply. At least building your own you have the option of using some quality cells that might last a while.

    1. Yeah, but if you search for “power bank without cells” on eBay you can find exactly that, for 3 USD you get housing, charging and step-up board with protection, LCD display and LED flashlight. Only thing you have to do is find and put cells inside. I usually do so because I have bunch of barely used 18650s from laptop batteries. In the featured project only circuitry and board costs 3 USD, and housing have to be 3D printed, so few bucks more.

    2. You can try balancing the cells. If one gets out of balance, the charging stops too soon, and it gets worse with time. Charging in parallel is fine if the cells are matched and balanced. Parallel banks rely on this. It SHOULD take years of use to become a noticeable problem. But if you are starting with bad laptop packs, it seems pretty likely to go bad quickly.

      1. No, you do not need to balance parallel connected cells. They balance at the moment you connect them in parallel as the voltage equalizes. Of course you should not connect cells of very different state of charge in parallel because momentary high currents could occur. But once they are connected in parallel and stay like that they are at the same voltage (balanced).
        Balancing is only an issue in SERIES connected cells where cells of different capacity get the same current and one reaches its end of charge voltage before the others.

        1. Interesting and good to know. In reading data sheets for charger chips, I thought this was a problem. This means I can go ahead with a battery backup project without getting complicated. I have a bunch of 4 cell 18650 holders for PCB mount just waiting.

    3. But this TrustFire or UltraFire cells are the opposite. They sell you “4000mAh” or even “9900mAh” cells which really have less than 2000mAh, sometimes even only 1000mAh and high internal resistance. Them being either factory rejects, recycled old cells or deliberately made fake or extra cheap cells with much less active material in them. In the latter case they are much lighter in weight than real 18650 cells. EEVBlog or bigclivedotcom did some teardown of such fake cells which were labeled with “9900mAh” and were quite weak light and hollow. I think that in reality no 18650 cell with more than 3000mAh exists and these are only expensive name brand cells like Samsung.

  4. With those UltraFire cells that 4cell powerbank probably doesn’t have more than 2000mAh. Those are extremely crappy cells, and they’re usually around 500mAh, nothing close to those 3000mAh written on them.

      1. I just received a programmable load and I have a selection of shunts, plus a good variety of eBay 18650’s. I’ll do some testing soon, and compare to the claims for some Turnigy transmitter batteries that use a balanced charger.

          1. The Turnigy packs are series. 3 cell 11.1V. They are not made for high current, which is fine. I’m more interested in battery back-up than running flashlights.

  5. Sometimes I think people just don’t understand the point of being able to build something themselves. Sure you can go and buy some Chinese crap for a couple of bucks, but you won’t learn anything. I use a similar project for ham radio. It’s also based on 4x 18650 batteries, balance and charge controller, 12 output, with simultaneous charge through a power supply or solar panel.
    Julian OH8STN

    1. I agree with you, but your project is much more complex, interesting and well engineered. You considered which protect board to use, which voltage converter, you choose excellent Olight cells and made powerbank that outputs some serious current at non very standard voltage (for powerbanks). So you basically made something that’s not so easily available, at least not for that price. Great job man.
      Featured project is just powebank module put into a box, not much learning, and result is just as bad as any cheap Chinese powebank, but with more money and time spent.

  6. “This DIY USB power bank packs 18650 battery cells”

    Man, that’s a lot of cells. :D

    Seriously though, nice to see there are options for making a custom power bank cheaply and easily.

  7. I’m surprised to see the community not rebelling against the claimed “16000 mAh” rating. This is at 3.7 V so when it is a 5 V output, that drops down 74% to 11840 mAh.

    1. Yeah it’s one of my pet peeves as well. Especially on a commercial product where you only ever see the 5V output, the rating should reflect the amp-hours at 5V.

  8. Ok so I have bought a 8 battery usb power bank case it’s I am going with quality and max mah I can find but I’m not sure if I spend extra and get high amp load batteries if it will be any different from same mah but lower amp load at lower cost like the usb power output is 2.1A I think those batteries cost a quarter the price same quality of brand just they have an amp load of 10 my other ones identical mah but 20A continuous discharge but cost the same as 4 of the lower amp load will I benefit from the higher amp load batteries at all considering it is only 2.1A output? Or would it not make a difference and just be a waste of money as the cheaper batteries with 10A load are higher then the power bank max amp load output anyway and won’t even be fully getting utilised either im guessing? They are all good brand vape mod rated 18650 just amp load and price differences lol

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