So, after having posted on social media about the boxes I built a finnish friend reached out to me asking for help in printing a box. He already had a design and proper 21700 batteries so I just threw something together in CAD and printed it out for him.

When I asked him for a logo to use he sent me a picture. I don’t know if he was serious or not but this is how it turned out:

He was happy with the result and the fit in the frame was more or less perfect.

Didn’t get many more pics of this project unfortunately, so this was just a quick update.. there’s still much more to come so stay tuned!

So, a buddy from Italy reached out to me. He had seen what I’d built for myself and my family and had a super nice Mondraker frame for which he could not get a suitable battery case. Since it’s almost impossible to ship batteries abroad I offered to make him a case for him to weld his own pack in.

Same method as before but he wanted to fill the entire frame “triangle” on the bike with the pack, so we made quite the large compartment for the BMS and wiring. This was also done to minimize the total width of the pack and centering it on the frame.

Here you see all the components. The cell frame, the joiner, the sides of the box and the TPU gaskets to make it waterproof(er).

Since my buddy didn’t want visible zipties to mount the pack to the frame we devised a mounting system using CNC milled aluminium brackets to mount to the bottle holder holes and two additional holes he would make.

The brackets are made to make the plastic case survive the forces from the M5 screws holding it to the frame.

Perfect fit. The bit wierd method of having theese brackets under the box is so we could use the cellframe/joiner method to make it. The brackets are mounted on the frame and the box slid over them before putting the final side on the box. That way the box can be removed without tearing up the cell welds. 😉

To be able to make the logo more visible I printed white infills.

This box is now in place in Italy enjoying the sun and I got a picture of it all mounted.

Beautiful bike and the battery fits perfect in the frame!
This was quite an interesting build. The design my pal had already done and he had quite specific requirements for the mounting system and how he wanted it all to look. Turns out he knew what would look awesome in that frame!

So, of course when I ride an awesome ebike the kids want one too. First of all I had to build one for my wife but that’s just a standard bike with a hailong pack. This is what I was riding at the moment:

Generation 1, 2020

But since my son was a wee bit short (10 years old) the bike we got for him could not fit any standard battery, so this was actually the very first totally custom battery I built.

Started out by making a dummy frame just to see how many cells we could fit in his frame and to get an idea of the shape of it:

Made cell frames and fit K-power 2500mAh 12,5A cells in there.

Installed the second frame and welded it all together.

As you can see this is a 13s5p pack yielding a whopping 48V with 12,5Ah and a total power output of 62,5A. This is by far enough for a small 10yo child. Only once did he ever run out of juice with this battery and that was after a 40km+ ride starting out with a half full pack.

Kapton tape to insulate the pack and then it was just a matter of mounting the BMS and putting it all on the bike.

Printed the case on glass, that’s why the sides of the box is so reflective. That didn’t last for long with the abuse the kid put this bike through though. 😉

Generation 2, 2021

Skip forward one year. A couple of crashes later he has grown quite a bit taller and now enjoys following me on the harder offroad and downhill trails. Never complaining I can see how he suffers from the stiff rear end of the green Merida bike and having bent both the rear rim and the front fork quite badly I thought it was time for an upgrade.

I found a used Giant Glory 8 in small size for cheap, just some 350km away, so I made a roadtrip and picked it up. This frame looked like a perfect fit for an electrical conversion!

After some careful measuring (and a lot of not so careful grinding on the frame to fit the BBS02 motor) the normal process started.

Cell frame with cells. This was actually the first time I tried the frame-joiner-frame pack type due to a total lack of space in the frame. This time we wanted more speed so we decided to go with a 14s4p pack to get a 52v battery. The problem using only 4 cells is the low capacity of the pack so this time we built it on LG MJ1 cells with a 3500mAh capacity and 10A continuous power output yielding a 52v pack with 14Ah capacity capable of 40A output. This is more than enough for the BBS02 and even after upgrading to the BBSHD (after messing up a controller) the battery doesn’t even sweat power wise.

The joiner is installed over the frame with cells. Take note on the cell configuration. I’m trying, even though it’s sometimes hard, to get as good a serial connection as possible throughout the entire pack. For a 40A pack like this I want to get at least 4 or 5 serial connections with my 0.2 x 8mm nickel strips which means I often have to put several layers of nickel on top of eachother.

Other side cell frame put in place. It’s such a tight fit that I sometimes have to put the pack on the floor and use my weight to evenly push the frame onto the cells.
Welding and adding insulating kapton tape on the side of the battery before turining it around to weld the other side. I take real good care not to accidentally short the pack out. Shorting it out is REAL unpleasant and bad for the cells too..

After insulating the pack more with tape which I like to put between the cells and any leads running over it, I add the BMS to the side of the pack and then close it all up.

He did not want any logo on the side of the battery so this is how it turned out. Works flawlessly but 14Ah is a bit on the low side with the type of riding we do now so for next summer we’ll revisit this bike and somehow fit an even larger pack on there.

So, a couple of friends wanted to build ebikes of their own and of course they needed custom batteries to fit their frames.

Specialized – something

The first one was easy, some sort of Specialized bike without rear suspension. The problem with theese bikes is to build a battery that looks good in the frame.. I had built a battery earlier that he liked but wanted to increase it from 13s5p to 14s5p, so I printed an extension..

Here the pack is welded, the BMS is soldered and mounted on top – only the power leads left to fix.

The battery cover is mounted. Here I used 6mm aluminium rods that I drilled and threaded to hold the box together. Later on I found M5 thread inserts that – when mounted correctly – bonds great to the plastic print. Much less work and a better result.

Mounted in the frame the battery sits like this. Looks more or less like a standard battery, nothing special but it works. 52V 12,5Ah and a cont current output of 62.5A is enough to power most anything for quite some time.

Mongoose

Now this frame is an odd bird..

Unfortunately I didn’t get any pictures of the frame while it was here, so this’ll have to do. The suspension on this frame works in a really wierd way and there’s virtually no space inside the frame to build a battery, so we had to place it underneath the frame.

When making a battery like this the first thing I do is, like in the picture above, take a picture of the frame as straight from the side as possible with a reference measurement in the picture, like the caliper taped to the frame above. That way I can import the picture into Fusion360 to start design of the battery box.

I then figure out the cell placement and the overall shape of the box and design the battery cellframe. From this drawing I make a PDF that I print on regular paper to test fit in the frame and when the fit is good I continue with the CAD.

I make a 3D design of the cell frame making sure the cells will fit in the holes and that there is room for the BMS and all the cable routing. I also make sure there’s room for the bolts, or in this case we used zipties to hold the box together. When possible I try to make sure the layout of the cells is such that good power transfer between the cell clusters is achievable when welding the pack.

Next the Joiner is designed. Now the outer shape of the battery takes form. When possible I try to make brackets on the joiner that fits the frame for the most secure mounting possible. Channels for zipties are added to the design to make mounting easy and secure.

“Rubber” gaskets are designed and finally..

.. the outher shell, or sides, of the box is designed. Custom logo added on demand. 😉

After this it’s just a matter of letting the 3D-printer do its job which usually takes 40-60 hours for a box of this size.

After the printing is done the cells are added to the cell frame, the joiner installed over the bundle and the second cell frame mounted on the other side. The cells are then welded taking super cautious care not to short anything out and then after the BMS has been added, the sides are bolted on and the pack ready to go on the bike.

For this pack I tried using zipties instead of screws to hold the box together. It works fine but looks a bit wierd and after finding the threaded inserts that’s the way I’m building packs further on.

Unfortunately I do not have any pictures of this pack on the bike. Will try to get some the next time we ride together!

Well, more packs and builds to come. Please leave a comment if you appreciate the build posts, or send me a message on social media or discord.

So, the first eBike I built for myself was a Canyon AM 8.0 which I first installed a BBS02 on and upgraded to the BBSHD after a month or so. Since my wife didn’t think I should make everything myself I bought a hailong battery with 13s5p LG-cells. It worked but the way I was riding the bike I could not find any method of getting the battery to stay on the frame. Eventually there was a combination of custom aluminium brackets, zipties and electrical tape which.. well, it wasn’t really my style.

Since I was 20kg heavier back then and the AM wasn’t really made for the kind of riding I did I eventually got an ok to upgrade to a used Radon Swoop 200 I found online.
Since the shape of the swoop frame doesn’t allow for a standard battery and since I wanted as much capacity I could possibly fit in the frame..

RunstenRacing battery version 1.0
Amazingly I fit 98 cells into the frame making this a 14s7p battery with a huge capacity of 24.5 Ah and almost 1.3kWh.

This frame however did not allow for mounting the BBSHD in any good way so it was pointing straight down. With 200mm of travel there’s not much room under the chainwheel when fully compressing the suspension on landing. After having been thrown a couple of times over the handlebars due to the motor hitting the ground I eventually “upgraded” to the CYC X1 pro. The style of mounting of this motor is much better suited to my style of frame.

Well, the CYC with the BAC855 can handle 72v..

RunstenRacing battery version 2.0

I really don’t know how, but I found room for 2 more cells rendering this a 20s5p battery. Since the 50A cont output of the MJ1 in a 5p configuration is not enough for the BAC855 I upgraded to SonyMurata cells capable of 35A each giving a total of 175A continuous power output – which is INSANE. The downside is that the Sony cells only had 2600mAh capacity, so this battery was a 72V battery with 13Ah capacity, or almost 0,95kWh. A lot less than the LG cells would have given but you can’t have a battery that’s not up to the job!

Well, since I wanted a lot of power output I bought a DALY BMS, 100A and 20s. That’s the red thing mounted under the frame. It was too big to fit inside the battery in any good way. This was a bit awkward but it worked, for a while..

One day the bike just wouldn’t turn on. Turned out the BMS was fried for some odd reason! Well, now I had no way of balancing the battery cells so..

RunstenRacing battery version 3.0

New design, new detachable mounting system with the same 20s5p layout using Molicel cells with the same 35A output and 2600mAh capacity as before. This time I bought a cheap BMS that fit inside the battery. Since the maximum output of that BMS is 30-ish amps I simply didn’t route the power cables through the BMS, so it’s just for carging and balancing the cells. Works flawlessly.

I really like the new design too but the mounting system is just too much trouble to be worth it. I won’t make another battery using that.
The idea was to have a battery that was easy to remove so we could build extra batteries to charge while we were riding so we could simply swap batteries when empty and go on riding.. This is still an idea but this mounting solution isn’t good enough.

So, since there seems to be an international interest in the eBike batteries I’ve built for myself and friends I’ll post some pictures of batteries, cases and give a bit of insight as to how I’m designing the cases.

I’m thinking I’ll make one post for one or a couple of batteries. That way it’s easier for me to post something a little now and then, and it won’t be a massive boring post of all of the batteries and iterations I’ve built and taken apart. 😉

So, enjoy, or just skip to something else!

So – one of the first custom batteries I built was for my brother.

So, of course there has to be a logo on the case, but since we couldn’t figure out what to put there he got the standard.. 😉

This is a 52V 14s7p battery with LG MJ1 cells making it a whooping 24,5Ah and almost 1,3kWh – which is insane for an eBike!

As you can see there’s the cell frames into which the MJ1 cells are mounted and welded. On top of that there’s kapton tape to protect the connections from shorting out. Then there’s a frame – a Joiner I call it since it joins the two cell frames together. On top of that there’s a TPU gasket to make the battery a bit more waterproof, and then there’s the top piece.

After adding the balance leads I used proper electrical tape to further insulate and protect the cells – something I’m not doing anymore since it makes the size of the battery too hard to predict. Also adding more kapton gives a better protection and a neater size.

The battery mounted in the frame of his Radon bike, propelled by a BBSHD motor. At 70A continous power output this battery is pretty oversized for the application but it gives a good range.