The proper way to solder 18650 cells!


I procrastinated many weeks about whether or not to solder 18650 batteries. I tried many combinations (solder, wire and flux / acid) to find the quickest method to solder these cells together. I’m pretty proud of the outcome (less than one second contact time and to tear the connection apart you need really significant forces and the battery can gives up millimeter or two when applying a huge pull)

Items needed:

  • A quality 80w soldering iron
  • Lötwasser (soldering acid)
  • Stranded copper wire, I took mine apart from an audio cable
  • Leaded solder
  • The actual cells

What I couldn’t demonstrate in the video is how I applied pressure to the joint with a wooden block to really maximize the surface area of the contact. Please enjoy the short video!


I’ve soldered wires to nickel that is welded to a cell but never a bare cell.


That is a totally different story, especially when theres 2-3 layers of nickel But still soldering is not the solution because to get proper connections the cell needs to get to like 250c or something


Immediately after the connection was made I could place my finger on top of the joint and believe it or not the contact was only slightly warm. The real reason I’m not using a spot welder: cost…

run away from your board when it sets itself on fire :smiley:

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boss level is less than 200$ with the battery to power it, not that expensive if you make more than one pack or sell it after


Agreed with decky and acido. While we appreciate your efforts, this is a dangerous method and is not worth the risk


@PatRocks Is there a specific reason why would this be a dangerous method as I’ve cardboard-insulated the positive terminals (and sure as hell the copper won’t melt through cardboard no matter what).

Is there something else that would make this a dangerous method?

This is a demonstration on how flexible this kind of installation is. Leaded solder can also withstand the huge forces on a crossbow’s bow’s tip… Torsional forces are probably something solder can’t withstand but I don’t see how the contacts would come loose from the 18650’s.

And yes I’m aware of the fact spot welding is a bit safer but I find it interesting to really understand the real differences between spot welding and soldering if done right. Thanks for the inputs guys!


The damage that can be done to the electrolyte by the heat, even for a couple seconds of contact, can mess with the properties of the cell. It can change the internal resistance of each cell, leading to (best case scenario) a pack that drifts more than usual. Additionally, it is risky in terms of electrical connection and may be a critical point of failure. If the contact is compromised, may result in arcing, then heat, and possibly fire. I would never attempt to build a pack without a spot welder.

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@PatRocks Is the small difference in internal resistance how relevant as some people have even successfully built well-functioning packs with different cells from different manufacturers. Correct me if I’m wrong - parallel packs (1s6p) difference in cell resistance won’t matter so much as the parallel cells are always forming one pack with precisely the same voltage.

And my intention is to never assemble a BMS. I’ll always balance charge the pack and monitor it externally and I’ll set the low voltage cutoffs etc to the VESC and in addition I’ll use low voltage alarm buzzers.

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@PatRocks Do you mean that the copper would come apart from the cell by “compromised contact”?

wtf, so much hate. Atleast he did it the proper way, been done plenty times before without significant harm to the cell (if you know what you’re doing obv.). Looks solid, good work!


Raptor 1 deck has 0 flex but it’s actually conductive because it’s carbon so may be even worse for this application lol

I dunno man I’m 300lbs and the thing will not budge. If it has any flex then it’s not measurable with out scientific equipment lol. Btw very uncomfortable to ride.

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Yes, because molecules stretch. If you stare at them long enough.


You know what else stretches? Belts.



haha, do you guys wanna see the mess i made soldering? turns out good leaded solder has a hard time sticking to cells

These cells are a goner and I’m pretty sure if I paid @psychotiller or @hyperion1 good money to build a pack out of these they wouldn’t

The flux is hard after to clean off almost impossible

IMG_20190311_203112 IMG_20190311_203147 IMG_20190311_202645

@FinnishSnowmobiler I’m on your team! Most of my packs have felt the heat of a soldering iron. Skinny strips of nickel just ain’t enough! :slight_smile:

I look at my A123 26650, and look at the .20 nickel, and I just can’t bear to do do it. 3 packs built with solder, no problemo. I really think soldering is the correct way to go with low p count packs built from high power cells.


Ay don’t insult thin nickle strips, even though I’m biased and I perfer thickk nickle strip 2x 0.30 most people would do , 3x 0.15