An Exhaustive Guide To Building 18650 Packs

Most of us know the basics of building packs of lithium-ion batteries. We’re familiar with cell balancing and the need for protection circuitry, and we understand the intricacies of the various serial and parallel configurations. It’s still a process that can be daunting for the first-time pack-builder though, because the other thing that most of us know about lithium ion batteries is that getting things wrong can cause fires. Rule zero of hackerspaces is “Don’t be on fire”, so what’s to be done? Fortunately [Adam Bender] is on hand with an extremely comprehensive two-part guide to designing and building lithium-ion battery packs from cylindrical 18650 cells.

In one sense we think the two-parter is in the wrong order. Part two takes us through all the technical details and theory, from lithium-ion chemistry to battery management systems and spot-welding nickel busbars, while part one shows us the construction of his battery pack. There are also a couple of videos, which we’ve placed below the break. It’s still not a job for the faint-hearted, but we’d say he’s produced about as professional and safe a pack as possible.

If spot welding worries you then it might be possible to build a pack without it. But it’s always worth considering: would you be better served buying one?

21 thoughts on “An Exhaustive Guide To Building 18650 Packs

  1. C rating definition in the second video definition is incorrect I believe (he says 10C 3Ah battery has a 10/3 discharge rating, where in fact it is a 10*3 discharge rating), also no fusible links on the cells so if one cell in a group develops and internal short, well, it might get exciting with high current cells.

    1. Direct links to cells (not a fuse for each) is by far the most common way of doing it, and this is normally not a problem with just 4P. It is used when you have massive cells in parallel like in electric vehicles, but not for small packs.

      1. It’s always dangerous when you have more than 1 lithium cell without a fuse. All it takes is for one of them to go bad, enter a low impedance state, then the other battery discharges through it causing a fire or explosion.

        With more batteries comes higher likelihood of failure, but with only 2 batteries you can also cause a fire. It seems like most young hackers don’t seem to understand or care about the consequences of sticking even a few 18650 batteries together.

  2. This lands perfect on my feed right when I’m trying to rebuild my scooter battery for air travel.
    To anyone that perhaps can share their knowledge or feedback, I want to turn my cilindrical 5.4AH 36V 10S2P 18650 pack, into a 3D printed, removable cell for 5AH 10S1P 36V 21700. Any thoughs or suggestions for this endeavor?

  3. le sigh, my want for an actual write-up and not more video. I get that this is how people make money now a days but it makes it so hard for the viewer to find the relevant information to them.

    1. Seconded here.
      I know that it is more work to photo and document a project properly, but i use most of my references like this as a quick reference guide to search for that one detail I couldnt remember when I needed it.

    2. As a partial solution, you can open the transcript on youtube and search in it. With native english speakers and good video quality, the automatic captions are quite good.

  4. This wont work on naked cells as the flat ribbon wire shorts + to the negative case.
    I do prefer Tesla style passive fuze to each cell (0.5mm resistor leg) instead. Can be soldered easily, damaged cells can be replaced within minutes, is dead simple and safe. No BMS needed, and so is much cheaper.
    However, that requires hot glueing the cells together which brings own pros and cons.

    1. Bad advice here. A BMS is ALWAYS required with lithium batteries, even if just one or two cells. This is why any laptop battery, for example, has one. They may only have a few cells, but they still have some type of BMS installed.

  5. good thought but how you choose fuses? which of the many currents do you take in to account?
    nominal, max continuous discharge, max current for 10s, some other current maybe?
    In general I agree that unprotected cells should be fused, we can discuss the method.

  6. looking at building a 12v 15ah SLA replacement from 18650’s cells. space allows me a 8×5 configuration. i need 12v ideally as circuit was designed for SLA, however hope to have a BMS between that and cells. ideally 4s is the best for SLA 12v replacement as 3S would not fair so well. Any suggestions on BMS boards for 40cell array? I’m keen to not turn this into a fireball. I’m also looking at LiFePo drop in replacement, but have a large number of laptop cells available hence asking here.

  7. Hi and thanks for the great video. Do you have any info about the BMS, what kind, where to get it, etc.?
    Did you make another video on BMS’ that I don’t see?
    I have an existing battery that appears to have a bad BMS and I’d like to replace it Basically build a new battery with existing parts and cells. Any info or suggestions is greatly appreciated.

  8. I am interested in building a battery pack (or more accurately, have already put together 5 packs with cell holders that require indivual cells to be recharged separate) to power a Power Wheels car for my grand daughter. I am desiring to build a single cell that can be charged in the car using a plug in charger. I think I have found the guide to get me started in the right direction. Thank you!

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