Modular Battery EMTB - Swappable 12S2P/3P/6P

Both long range and jumpable! The best of both worlds, all because of my obsession with swappable batteries.

…mind the burn marks on my floor. I had a LiPo fire a couple years back…

The board is an experiment of sorts. I was highly inspired by @rich with his jump boards and I wanted something light-weight, but I didn’t want to sacrifice the range. After experimenting with a swappable battery on my cruiser board I went about designing this, which gives me all that I wanted. It has two battery harnesses with two completely modular 12S3P battery packs. When both on the board, the batteries are in parallel and give a combined 1 kWh, but the board is getting close to 45 lbs. Hard to jump in this config. When I’m just running a single pack, the capacity is halved and the weight is a lot less at just under 35 lbs, making it very jumpable.

Battery Modules:


  • 12S3P Molicel P42A 500 Wh
  • Rated for 75A continuous with a max of 90A
  • Bypassed smart BMS w/ BT.
  • Fuses integrated into the Nickel designed to blow after 5 seconds at 105A. Hopefully these never blow because they would be a bitch to replace.
  • Charge port fused for 10A on each pack. The C- also has a port on the bottom. The goal with this was to allow the parallel packs to both balance if a charger is plugged into one battery rather than one battery balancing and the second battery being charged through the parallel connection. In retrospect this is unnecessary since I can just set the BMS to static balance and allow one pack to bring up the voltage.
  • Loop key kill switch to disconnect the positive from everything including the charge port. This is used to turn on and off the board.


  • Splashproof with 1/8" rubber gaskets on the side and in the access panel on the front.
  • VERY snug fit for the actual battery The overall dimensions are 190mm long x 130mm wide x 85mm tall. The top and bottom are 5mm thick so it only left me 5mm of space for nickel strips, foam, balance, wires, and the actual terminals.
  • Fastens to the board with 4x M8x70mm bolts. There are 4x M8 washers and locknuts epoxied into the bottom of the deck that these mate with.


Battery Harness:
The harness has an integrated xt90 and 5.5mm bullet connector that mates to the packs. The bullet connector connects the negative terminals of the charge ports together, while the XT90 connects in parallel to the VESC. This is a tight fit already, but is secured with the 4x M8 bolt. The harness is 15mm tall at the lowest point of the concave of the deck, and 8mm tall at the highest point. The wires are completely waterproof inside, since I epoxy-coated the entire inside of the harness.
It is fastened to the deck through 8 M6 bolts and threaded inserts.

The Board:


  • MBS pro 97 pre-build w/ heel straps
  • BN matrix II motors mounts
  • TB 6374s
  • Flipsky dual 6.6 (the big one)
  • VX2


  • 52 km/h top speed
  • 18-30 km with a single battery, 45-65 km with both (less sag with both batteries gives a fairly significant increase in range)
  • 90A/-24A with a single battery, 150A/40A with both.


  • I’m done with belts. Went through some snow early this spring. It got in the belts, stretched them out and snapped them both instantly. So annoying. I can imagine this will happen in the mud off-road as well, so as soon as @moon restocks I am ordering some moon drives. Will update when those come (if I can order quick enough to get them).
  • I am also aware of the issues associated with charging in parallel, since if cells are out of balance in one pack, then I run the risk of overcharging that pack since the BMS cannot cut-off the charge due to the parallel connection. I regularly check the balance of the cells through the BT app though so this really isn’t a big deal.

If anyone is interested in a detailed parts list and STL files, PM me and I’ll help you out.


This does suck a lot.


Those modular battery holders are amazing! Awesome to see people innovating :smiley:

I’m guessing the 3rd bullet is meant for charging the packs through the BMS, yeah?


Really does. At the time I only was carrying one spare belt too so I had to limp my way back home.


Thanks! And yeah exactly, connects to the C- of the BMS. Though it is pretty useless tbh. Would’ve been better to have just the XT90.

1 Like

I’ve changed a belt on the side of the road, only to have it snap again in the snow five meters later. Super annoying.


That’s some bad luck for sure… at that point it starts to become cheaper to just go all in and get gears. The cost of the belts adds up quick, even at Ebay prices.

Steel gears weren’t available until recently. I won’t do plastic gears again.

1 Like

Super clean battery swap execution. This is a fantastic build :+1:


I’ve been dreaming for year for a modular battery pack similar to what the Loaded X Unlimited kits do

You nailed it! Especially for an MTB design.

If i do have one suggestion i’d be that you really need to redo your soldering.


Those look like good hot joints to me. But IDK :man_shrugging:


No? POM doesn’t hold up? I would go steel but can’t get them with helicals. I need helicals.

Thank you! It means a lot coming from you!

imo Revel has it down in terms of modular packs. Loaded looks cool and I’m sure works well but those batteries are tiny.

Yeah… I mean they aren’t cold joints for sure. My soldering iron is chunky as hell. But I could’ve added more solder on the left one there. The right joint doesn’t really need to be great though, A max of like 2A goes through it. Whatever though, nothing I can do about it now. It’s all sealed in epoxy.


:rofl: :rofl: :rofl:

1 Like

Solder only has 10% the conductivity of copper, so you really want as much wire to contact the connector as possible and only use solder to fill in any gaps and hold it in place, rather than using solder itself to connect the two electrically.


Oh yeah I’m aware. But like, context.

There is less than a mm between the deck and the end of the connector so I couldn’t shove the wire deep in there, had to put it on the side. Hopefully since it’s not very far that extra resistance doesn’t heat it up much, or if it does then the 10AWG saps the heat away. I’ll check the temps next time I take it out.
Didn’t know that it has 10% the conductivity though… damn.

Also, RIP:


Thanks man, feel honored :grin:

Great idea and implementation of swappable plus divisible batteries, awesome!
For jumping I would use the front pack for better balance of the board.

M8 seems overkill but why not (or maybe there is a reason I don’t see). Do you use any rubber washers or something else like springs to avoid loose bolts because thread locker is no option? I am working on swappable packs as well and this is my main concern.

Especially the DW II is merciless when it comes to vibrations. All bolts came loose several times within each single ride in the woods until I used more and more and then a ton of thread locker.

I love and hate the DW II. I love that you have so much control and direct feel. I hate that it is stiff as a concrete wall, after every ride I have a concussion :joy: . But I have to say it is very much related to the stiffness of the tires. 9" T2 nylon tires are unfortunately very hard and even uncomfortable on a bouncy Trampa deck. 8" T1 tires on DW II deck feel like riding on clouds in comparison which is really weird but also great.

Regarding POM gears I wouldn’t worry too much. I abuse them hard e.g. climbing really steep hills which I would never do with belts. I had one single damage within 3 years and it was my fault.

I would say enemy number one is too much backlash.
Second if you jump then you MUST avoid touching the throttle during landing (let it go shortly before take off then it’s best). If you hit and hold 100% brake during landing then your gears won’t be amused but this applies to all types of drivetrains. I also interrupt accelerating on heavy cracks or bumps no matter if gears or belts.


Those videos of you flying off jumps really got me started, so thanks for that!

Okay so this comment made me realize I forgot to loctite the M6 bolts holding the battery harnesses on. One bolt on a battery harness was actually loose already… I just went and put a ton of the 243 blue stuff on every bolt and I don’t have any rubber washers or anything so hopefully that will hold. If they keep coming loose after this I will put a layer of the 1/8" rubber gasket between the harness and the deck to act like a rubber washer.

The M8 bolts are definitely overkill, but I think better over than under. I haven’t had any trouble with them yet. The M8 nuts in the deck are locknuts so loctite isn’t really needed. The locknut will eventually wear out and I’m hoping then it will still be okay because the plastic enclosure will hold it in place.

I have never ridden another MTB deck but I am loving the DW so far. The landings of jumps is so stable! The heel straps really help in this regard too, though it’s a double-edged sword. With the heel straps I worry about falling since I know I’ll severely mess myself up if I do but I also feel that I won’t fall as easily since I have so much more control. The deck is super stiff but I honestly prefer it, same with streetboards. My streetboard is flexible and honestly I find that the flexibility does not dampen any road vibrations at all and can even make it worse. I assume this is also the case with MTBs but idk.

This is reassuring. Why’d they break?

Though Boardnamics seems like his drives will come out quicker so I may get some of those, with the bonus of getting metal helicals. I’ll decide tomorrow when they come out.


That should work :ok_hand:

Damn that’s pretty smart, nice!

I worry about falling without :man_shrugging:
I know what you mean in the beginning it feels like a handicap and very weird but soon you can’t ride without. For me falling is much safer with heelstraps and more predictable (and saves my knees from twisting). But you definitely need a protective vest to save your back, front, shoulder and arms and good gloves then usually nothing bad happens.

I had many crazy falls but never a really big injury. My biggest problem when falling is that I always try to catch the fall with my hands which lead to several shoulder and arm problems and months of pain. I will practice falling in the meadow without arms and see if it works. I’m too old for this shit :joy:

Then it seems it’s the perfect deck for you, probably the stiffest on the market.

In my case a bad combination of askew drivetrain, too much backlash and unintentionally touching the throttle during landing (almost crashing) in dirt park. Until then, I thought it was a rumor that gears could break :sweat_smile:.


Yeah I’ve heard this is a must. I have the flatland gloves and a decent helmet but I really need to just put the money down and get good gear. I’ve been putting that off because even though yeah it’s necessary, it ends up being a good quarter to a third the cost of the board itself, so it’s hard to front. I will though. I feel like the most important bits are the knee pads and elbow pads for falling forwards, and back protection for falling backwards.

Still no falls yet though, and I’ve hit the local pump track a few times now. Can’t get too much air yet but I’m starting to be able to speed through the track. Man oh man is it fun. Only issue I’ve been having is when taking heelside turns through a burm. I just can’t turn hard enough on my heelside like I can on my toeside and have to manual a bit in order to make the turn. I think I might try to replace my heelside bushings on the matrix with the softer yellow ones and see if that makes a difference.

Oh… I can see this happening. I imagine you landing going full speed into a ditch or something and slamming on the brakes. I kinda feel like this is inevitable so I’ll keep an eye on my backlash and hope for the best lol.

Also about the gears, I decided I’m going with Boardnamics M1-AT with that sweet 5.2:1 ratio. I was on Moon’s website the minute batch 5 restocked but he didn’t have helicals so I couldn’t do it. BN has all metal helicals so hopefully in the worst case scenarios like what happened to you the gears being metal will save them.

Also, the swappable battery setup has been great so far at the pump track. I put both packs on on for the 10 km trek there, then once I’m there I take a pack off (the pack in the back), and it is crazy how much easier it is to jump. It’s like in baseball where you warm up with a weighted bat, then when you swing an unweighted bat it feels super light and you can just crush the ball. Same type of deal. You probably understand having taken both your jumpboard and the trampa one to spots. Anyway when I juice out one of the packs I unplug it but leave it on the board, pop the second battery on plugged in and ride home. Simple! I’m loving it!


I really like the modular batteries, so much I might steal the idea for the range extender I’m planning for my board

The initial idea was either magnets or a 3D printed latch system, but hey, 4 screws with a electric screwdriver won’t take even 30 seconds do install and will hold way better than the alternative

1 Like