Backfire, broken battery

So my Backfire G2 Black board battery would cause my bord to randomly turn of and then not wanting to turn on again, i’m getting a replacement from Backfire but tought that i could possibly fix this old one.

at first when i measured the voltage through the esc wire( the one that is going to connect to the esc) and the charging cable both were at 41v, but after i’ve opened the battery to check for any damage which could be the cause for the behaviour (short circuit or something) it is now constantly measuring at 16v

I’ve checked the balancing cable on the bms, pin by pin and all the pins have the same voltage so i know that all of the cells are balanced.

And when i measure the current directly from the battery pack i do get the 41v measurement. How ever, by measuring the positive wire directly from the battery and placing the other pin from the multimeter on each of the marked spot on each of these four things on the picture whatever they are i get a measurement of 41, except from the one makred red on the picture.

Does this mean that it could be this component which is faulty? so i can just replace it? Or must i buy a whole new bms?

It doesn’t look like there is any damage or shorted out component/wire from what i can tell, i’ve checked both sides of the bms.

What do you guys think?

Thankfull for any help!

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Could be a fried MOSFET. Those are a PITA to replace but not impossible. If you do attempt a replacement yourself make sure that its an exact match with the others.

Also you’ve probably heard of the Right to Repair movement. If you’re not up to the task you could look for a person or a shop who does that sort of thing. You could try contacting Louis Rossman or someone from his camp as well. Just a thought.

I see, i haven’t heard of it actually… probably since i live in sweden. But i think i can replace it myself.

If it doesn’t work, can you recommend another bms? could i just use any bms specified for 10s2p 36v?

i have tried googling on the serial code but can’t seem to find this bms on the market.

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Looking at the cables, you have B- (in) and two terminals (out) P- and DSG-.

I presume the P- (conneted to 16v MOSFET) is the charge port connection. So this MOSFET would actually only be to stop charging, and you are measuring voltage leaking. Then 16v is okay.

DSG- will go to ESC. This is cutting off the 3x MOSFET when you ride. This could be becuase of vibration making a cable loose, or a fault on the circuit board, or even a lose connection in your battery.

Most likely this is the BMS that is faulty, and will need to be replaced.

You could bypass this BMS by connecting DSG- to the B- wire, this will mean the cells are directly connected to the ESC.

You should still charge through the P- terminal, then if it does not charge, you know you have a real issue with your cells.

This will invalidate your warranty, and could be dangerous. I suggest this as a way to get going again, you are responsible for your own safety and skateboard. Waiting for your replacement BMS is the safest (and most boring) option.

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Hmm i don’t think there’s anything loose in the battery since i measure 41v from it, only from the bms i get 16 constant, before i measured 41 from it aswell. So whichever cable or circuit that was periodicly cutting off before must have broken completly now i think.

I think i will indeed have to replace the whole bms, since i also get 16v when i measure from the charging lead, this would make the charger think that it’s at 16v when in reality it’s 41v right? so i would still have that problem eaven if i fix the power to the esc by bypassing.

I’m actually getting a whole new batterypack, that’s why i’m trying to fix this one, would be a shame to trow it away because of a faulty bms…

Can you recommend any bms? or a brand or website?

And thanks for helping!

Yes it sounds like your BMS is damaged or unhappy with the state of the cells, since you measured a balanced pack manually then a BMS problem is most likely.

You could get a Daly or Deli Green BMS, they are small and cheap and decent quality.

They do not care how many parallel cells are connected, so a 10S BMS for Li-ion (important detail !).

Often we connect the cells directly to the motor controller (bypassing the BMS) to avoid this type of damage (and prevent the BMS being able to cut brakes). This means that the current rating you need will only be for charging, so only pay attention to that number and you can get a small BMS that should fit in place of the old one.

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Alright, My charger says: output:42v 1.5A

And this is my batterypack:

Could i use this one? Small Daly BMS (10S/12S/14S/16S) (The 10s version of ourse)

Or this one, It’s half the price of the Daly, Looks almost identical to the bms in my batterypack:

oh, could the bms cut the brakes? why would that happen?

So can i just solder the new bms on and go, or do it need to be programed or anything like that? (complete noob here)

And the Daly one says Max discharge current 15A, is that enough for my Backfire G2 Black?

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Ok this one I do know. Typically you’ll want to add at least 20% headroom in the BMS discharge rating for your setup. So if you expect 60a maximum go ahead and get an 80a BMS.

The other option is to get a separate port BMS that only handles the charging portion of the cycle. Then you let the esc manage discharge directly.

Daly doesnt exactly have the best reputation either. Will Prowse (youtuber) says their low temp cutoffs dont always work and other reviewers also say they’re dodgy.

Btw that battery pack you linked says it has its own internal BMS. So you wouldnt need a separate one.

That Amazon BMS does look like it’ll fit perfectly.

Assuming you are repairing a G2 board (for which this battery is intended), that has 2x400W motors, 800W / 36V ~= 22A. This isn’t an exact calcluation from motor current, but gives you a good idea your 30A BMS should be enough to drive your motors without failing.

If this were a ‘DIY’ board, and you put larger motors in there attempting to pull more than 400W per wheel, this would explain why your BMS cuts off. You can see from this picture the normal connections.

In a board with an under-rated BMS, you can connect ‘discharging’ straight to the ‘B-’ terminal. This means if you have a problem with your batteries or BMS, it will not cut off.

There are pros and cons to this idea,

pro: carries on skating with a BMS error.

con: Drawing too much current from the battery could result in skating a fireball.

Ultimately, knowing which cells you have and the ‘maximum current’ they can deliver is important, as if the cells are only capable of 30A, then a 30A BMS protecting them is probably a good idea

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Ok, I’m not sure how many Amperage of discharge i need, i got two 400w hub motors. how can i find out this?

Hm i see, what would be a better quality brand then? i Dont want my apartment på burn up because of a cheap bms…

Yes indeed thats the new one i getting from backfire, but the one on topic is my old one were the internal bms has failed, so the thing is i don’t want a separate one, i need to replace it completely.

Ok so the cells says INR18650-600, from wha ti can find they have a maximum continous discharge rate of 25A. And the cheap bms from amazon i linked i saw now has a ‘‘continous maximum current’’ of only 20A, so guess i have to look for another one. if i don’t Bypass it for discharge.

but i don’t think i’ll have to worry too much of skating a fireball if by calculating they should draw aproximately 22A and the Cells can Disharge 25A max continously, then it should be fairly safe too bypass right?

Would this work better? It says 25A:

That BMS has confusing specs, although it can work at 60Amps, it will cut off at anything above 18Amps (the last line on the table). Also, the B- tab is in a diferent place, I prefer your Amazon one as it looks more like your original.

Let’s say your Cells are 25A cells, you have 2P, so you can technically draw 50Amps before the batteries really have a problem, none of the BMSs you have found are high enough current to not eventually have the same failure, so as @kavic5150 says, it is better to have a larger BMS than you need to avoid this problem (as long as it’s still less than the battery limit)

I cannot really say what will work better for you, there are several solutions you could choose, all of which will get it rolling again, the rigth one depends on your own skill level, willingness to modify your board, and which replacement component you want to buy.


  1. Replace with the most identical BMS you can find (simplest as it should fit easily)
  2. Replace with a ‘well proven’ BMS (Deli Green, LLT, Daly)

Then either:

  1. Connect ESC through P- (BMS current rating applies)
  2. Connect ESC through 50A fuse to B-
  3. Connect ESC directly to B-
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What about this one then, It’s an LLT. Should be good right? there is a 10s 30a continous discharge one and you can change some stuff with bluetooth settings:

so maybe i’'ll go with this one and have both charge and discharge go through it.

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Yeah this sounds fine, the LLT is used by many skaters, and the Bluetooth App lets you monitor the health of the battery. This means if it ever does cut off, you can find out why.

You can see from the image they have many more MOSFETs, your original one had 3 for discharge and 1 for charge. This now has 10 MOSFETs shared for both directions.

When connecting it, remember that the metal sheet on top is meant to be getting the heat away from the middle, so put this facing the outside as mech as possible, will help to keep it cool.

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Yeah this one seems a lot better indeed.

I’ll remember that!

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So i’ve ordered the LLT bms. I’ll update you if it worked or if i need anymore help.

Thank you so much for taking the time to help me out, much apreciated!!

Take care guys!


So what happened with your Experiment @WalterWhite?

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