I opened a bad battery (weak) and cannot see BMS inside if this small chip can be a safe alternative?


1 µW
Apr 13, 2024
San Francisco
I bought a fat e-bike on Amazon.
Here is my review, this bike is a scam.
the only solution was to build the 2nd and 3rd batteries for that short-runner.
So I ordered plastic cases on Aliexpress and prepared LG MJ1 batteries to install.
Assembling the first battery, I decided to check where is BMS on the original battery was located,
because I expected the company, must follow minimal safety standards, perform tests, and find which location was better.
Opened the battery, I was surprised to see, it was no real BMS, but a very small chip&
I wonder if such a piece of micro microcontroller, can be able to successfully balance all the 91 elements?
If it is safe with the charging, driving, and staying in the garage.
There are many batteries made without balancing functions, because it saves them a tiny amount of money on each one. Unfortunately they also do this primarily on packs made of the cheapest cells that most need such a function to keep them all within a usable range, instead of rapidly drifting apart in voltage and no longer allowing charge / discharge.

There are also active-balancing BMS that don't have the per-channel shunt resistors of the common passive-balancing BMS, so they look more like the non-balancing BMS. You'd have to look up the p/n on the chip to find it's datasheet and see if it includes the active-balancing funcitons, and then see if the charge pump circuits are installed on the BMS board (if they're not part of the chip itself).

But a balancing function on a BMS has pretty much nothing to do with whether it's safe or not, just how long it's useful lifespan might be before it's too imbalanced to charge or discharge.

Safety is more to do with the actual cells used, the pack construction, and whether the BMS is correctly designed to protect those specific cells against overcharge or overdisharge or overcurrent during either C/D, overtemperature, undertemperature, etc.

But...in a cheap pack that doesn't even include a balancing function, it's probably less likely to be built safely of good cells and a properly specified BMS, and more likely to have parts not really capable of the label ratings, etc.
I am no bike mechanical genius, and certainly closer to the least experienced in e-bikes in this crowd...

But I am fairly certain that is not a dedicated frame you have, literally every bit of that kit is available after market... and I think I just recently saw an identical frame in a bone-yard...

One of the more experienced bike people might be able to verify it, I will ping the guy who lets me get bits from his boneyard and see if he can snap a pic of the frame...

I do know that exact suspension set up sucks monkley nuts, on the front end for hub motors, I tried a dual hub system as a test, and my 85 pound son was finding the front suspension to be "gooey like melted chocolate" so spongy, I brought it to a local bike shop that has a good mechanic, he said that is normal if you put a stresser like a hub motor on them. I have heard virtually the same exact detail here (this is where I hope Amber shows the amazing skill with the search system that still eludes my abilities)

How old is the bike? if it is under 90 days Amazon will probably make them refund you.
But a balancing function on a BMS has pretty much nothing to do with whether it's safe or not, just how long it's useful lifespan might be before it's too imbalanced to charge or discharge.
here is my conversation in Skype with a professional electrician
and certified Bosch mechanic Frank Schulz:

Soon will be a court with Amazon
I like to bring your expert opinion
that real BMS CANNOT BE SIZE of 25 cents

Frank, 9:31 AM
No, that's impossible
Sorry guys I still not making pictures.
Let me do it in the next 20-30 minutes.
You won't be the first guy
I am the guy who disassembles 50-100 batteries of all kind
and assembles 30-40 only big batteries(not count 12, 20 or 36 volts)
that's why I cannot miss BMS.
Sorry for not able to open it again, I ride far with extra battery.
Hope take the case off this morning