Making a modular battery - FAIL

EDIT: the design of this battery was a failure in several ways, however there is still good information regarding the techniques used to build a battery. Read at your own risk :sweat_smile:

Ok dudes, @rafaelinmissouri asked for a battery building walk through, so I said I would document my next build… although alot of this won’t be relevant to a standard pack, most of it will. On to it.

Start with your cells and line them all up to check the voltages. Most of the time the cells I get are between 3.41 - 3.45. If there is a cell that is way different, don’t put it in the pack. Put it in a torch, or a vape, or a dildo, whatever.

Glue those bastards together. Many people use hot glue. Many people use silicone. My personal favorite is polyurethane. Sika 11FC :ok_hand:

Once the cells are laid out, i like to lock them in by screwing down some timber.

I like to put the cells in a square jig and lay out each p group and then flip the next p group the other way around. There are 2 reasons for this.

Firstly, it makes it easier to see where to stop gluing (you only want to glue together single p groups at this stage)

Secondly, there is a ring around the top of the cells that is the slightest amount thicker than the rest of the cells and if you butt them all up together, they don’t squash up well.

Insulate your cells. The little rings of fish paper protect the negative outer circle at the top of the can from your positive connections. They are an absolute must have in any pack.

I have found a good source that has strips of 9 rings joined together, it’s definitely a time saver. You can find them here :
Keep the leftover bits of fishpaper, as they do come in handy. Often if I am folding nickel down the side of the cell or I think there is a small point that might receive a little more abuse, I will stick one of the little circles on that point and tape it down.

I like to fully wrap the p groups. Cut the paper to length making sure that you overlap by at least 10mm just to make sure you don’t fall short.

Start to wrap by centering the paper on the group and then fold around each side. This helps everything stay nice and square to the pack.

The paper I use comes in a 65mm roll, but there are other options for different cells too. You can find it here :

Design your connections. I generally have a good idea of how I’m going to build a pack, so I usually wait until now before I finalise it. It’s nice to draw your + and - on the packs and arrange them in the space where they are going.

Take a photo, draw your connections. I went through a few iterations for this pack before I settled on something I was happy with. There is no ‘best’ way to build a pack, every pack has different requirements so I will run you through a few of the things you should consider in your design…

Does the board flex?
If it does, your connections will need to allow for this. Silicone wire and braided copper are good options for flex packs.

How many amps is your pack going to push continuously?
You will need to know this to size your series connections adequately. There is a good thread here: Conductor Current Ratings [SRO]

Where will you run your main terminals and balance leads?
Be sure to allow enough room for your mains and balance leads. These may be on top or beside the pack or both, but it is an easily overlooked part of the design.

In my case, the board doesn’t flex, my connections need to allow for modularity and I have heaps of room to the side of the pack to run mains and balance leads. Great!

Once you have figured out your design layout and connection details, you should be able to determine the length and amount of nickel strips you need to cut. In my case, it is 80 strips at 50mm long.

I need 8 x 50mm strips for each p group, so I mark out 8 x 50mm intervals on my bench top.

I keep the nickel roll with one loose zip tie around it and can easily hold onto the zip tie while reeling nickel off the roll. Line the nickel up with the marks on the bench top and mark them.

After you’ve marked the 8 strips, cut them off as a group of 8 and repeat until you have your 10 strips of 8.

Cut the bastards up. Get your corner chompers ready. If you don’t have corner chompers you can easily round your corners with scissors. Or just be a rebel and keep your sharp corners (i don’t condone this type of rebellion)

All rounded. Be super careful of the little offcuts of nickel. Those motherfuckers are SHARP.

Time to weld. I am building this pack with bus bars so there is no need for me to weld a strip across the top of the cells. The bus bars will carry both the parallel and series currents and my design requires that these busbars sit on the sides of the cells, not the top or the bottom. So therefore I am using tabs.

To save on the amount of soldering i would need to do for 4 tabs, I decided to weld my tabs together. I used and offcut of the insulator rings we saved earlier and traced it onto a piece of glass…

Don’t weld on glass :rofl: it pitted after the first weld. I switched to a plate from the kitchen. It held up better but there was still significant pitting.

The problem with the pitting is that it can create a hollow underneath where you are trying to weld. If there is air below your weld, you will likely blow a hole in the nickel.

When welding to cells, I like to tack weld everything first. I try to only do one set of welds per cell per run. This is to minimize the amount of heat transferred into the cell.

I think that 3 sets of good welds per cell is ample. But they need to be good welds. A good test is to do one set of welds tacking nickel on a scrap cell (or a good one, but you’ll have to clean it) and then try to pull it off. If you can pull it off without tearing the nickel, you need to bump up your weld settings.

Next will be soldering but my phone is about to die…


Fuuuuck. Shit got ugly! Just a heads up, if you are looking for battery porn, you are now in the wrong place :rofl:

So this is where I am headed with the connections. Each pack needs to be a 2s4p and will plug into each other with 3.5mm bullet connectors. Each pack will also have a 2 pin connector for balance wires.

When soldering to nickel it is imperative that you scratch up the nickel before soldering. It will give you a far better solder to nickel connection. I use a dremel, and generally whatever bit is in it at the time :rofl: i used a cutting wheel for this.

Tin your nickel. You can see that I am using an aluminium strip here as a heatsink underneath my solder points. It works incredibly well to keep the majority of the heat away from the cells.

I warned you it was gonna get ugly :rofl: my initial plan was to use copper braid for this series connection to create the 2s4p packs, however, I tried on some strips of braid beforehand to solder directly through it and had issues with the solder wicking out to the sides rather than wicking through. I really should have persevered and developed a better method with the braid :rofl:

One thing i should point out about these connections. They act as series connections and parallel connections as well. The more typical way to do parallel connections is just to weld a strip across the top/bottom of the cells. I didn’t see the need since I knew my series connections could do the same job.

Soldering the bullet connectors to the short bits of wire that will form the parallel and series connections on the top of my pack.

I like to line up all my bullets in the third hand(s) to streamline that shit. There’s probably plenty of ways to do this, but i like to hold my iron up against the small hole on the side and feed the solder in from the top. Fill it nearly all the way to the top and keep the iron on it. Drop your wire in from the top and remove the iron by spreading it upwards, this will help to stop any solder running down and onto the bullet connection.

The ugliness continues. I stripped down the majority of the insulation so that I could make the 90 degree angle and also to minimise the height of the connection, as it is, this pack is gonna be tight for height.

I hot glued the bullet into the centre of the packs with the thought that this would be sufficient but it wasn’t :rofl: the heat from the soldering melted the glue and made a mess. But it held for long enough to get the solder in the right spot.

I should have mentioned it before, but working on this side of the pack now that it is a 2s pack is a little sketchy. I really should have insulated the negative terminals on the left hand side while doing my positive connections. But I like to live on the edge.

You can see what happens when you aren’t careful. Slipped with my aluminium heatsink and it touched the negative nickel and just burned straight through it :rofl: be careful out there kids.

Same again on the other side. Before I wrapped the positive sides up, I used Sika and slathered it over the bullet connector. This should lock it in place permanently. After I wrapped it up, i squirted a little hot glue in the gap between the 2 p groups to make sure there could be no contact between the positive and negative connections.

Added my balance connectors to the sides of the packs. I like to connect my balance wires to the negative side of the next pack along. It’s just habit for me. Gets a little confusing at times, but in a regular pack, it is definitely the way to go.

Temporarily tacked the balance wires down with kapton tape to get them in the right positions and filled in the critical points with sika. Once this sika cures, I can continue…

Next, up, final insulation and heatshrink :call_me_hand:


Ok so I’m totally bummed right now. The battery was a failure.

It didn’t fit in the deck! It was too tall and would have put too much pressure on the battery and the lid.

In addition to this, the connections were not great. As there was no flexibility in the connections, it would have been very easy for vibrations to work them loose or cause them to arc.

Sometimes you gotta know when to hold em and know when to fold em. This is a fold. Tore the packs down and it will now go together as a solid pack :man_facepalming::man_facepalming::man_facepalming:

There is still a lot of good information here, but just don’t follow the design :sweat_smile:


When you need to weld nickel to nickel, use an aluminium plate.
The nickel does not stick to it and it doesn’t pit under the weld.


I have tried this on your suggestion once before with interesting results…

I needed to turn the power on the welder up MUCH higher when welding on aluminium to get the same strength weld that I can get when welding on something else like a brick or a tile.

The alumimium seemed to suck the heat out of the weld and resulted in poor and inconsistent welds :man_shrugging:


Aluminum has a great thermal conductivity as you know.:joy:


It sure does! Check out my soldering heatsink for when i need to solder on tabs over cells :ok_hand:


Yes, this is accurate.
A ceramic surface is a very good alternative.
I just like the fact that the aluminium is more or less indestructible even if it requires more energy.


I also like it for that, but I like to weld fast, my kweld setup gets a little too warm for my liking when welding fast at high power :sweat_smile::fire:

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I tend to avoid nickel to nickel welds if I can help it.
This is why I mostly use H type nickel.


Yeah I can see the benefits of those nickel strips but I can’t bring myself to actually buy any of it. I like the flexibility to create the shapes I want just with strips…

That said, I am looking forward to purchasing a big fat roll of 25mm nickel :drooling_face::drooling_face::drooling_face:


…and than send me 5m over :stuck_out_tongue_winking_eye:


You are a good man Charlie Brown


want to build a pack but scared… will be watching this thread


Oh my god…
Now you tell me this after all this time struggling with taping up my rolls or having it unroll all over my bench…


Second post updated, one more to come :call_me_hand:


after all that work… battery building is not for the faint of heart :broken_heart:
(maybe turn this into a “how to reuse cells” thread)


Rip nickel off with pliers



Cut yourself

Dremel the little shards off the cans

Sink a few beers while the lipos charge

Start again :joy:


maybe you should switch back to Goat


Second picture on my last post… maybe the goat was the problem :thinking:

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