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Bionx Li-M n 37v battery pack rebuild attempt


1 µW
Dec 20, 2022
Hello all,
I’ll try to make this short: A man in my area posted a free bike on Craigslist And I got lucky and responded within 9 minutes. It is a pretty nice Cannondale with an after market Bionx rear hub motor installed by the retailer (I think). The guy told me he wasn’t sure if the battery was bad or the charger or what, but it was a perfectly good bike and included the original rear wheel so one could remove the bionx motor if desired.

I took it home and popped open the battery pack and diagnosed a fully dead battery, which wouldn’t take a charge. I believe they were 1500mah 18650 cells connected in 10s4p. I had several e-scooter battery packs consisting of NCR18650GA’s, which are either Panasonic or Sanyo 3500mah 3.7v batteries.
I set to work constructing a new battery pack, once again 10s4p and figure i should have double the range of the original pack.
I neglected to take photos and I’m having trouble connecting the charging port to the “BMS”.
Can anyone advise which wires go where?

Thanks in advance!


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Not seeing any BMS in those photos. They look like a circuit board. Sometimes there's a metal shell around it to act as a heat sink:

For Li-Ion battery chemistry they'll have a B- terminal for the battery negative, P- for the controller, and sometimes a C- for the charger. If C- is missing, the charger connects to the same terminal as the controller. They'll also have a connector for the balance wires with one wire for each positive end of each group of cells and sometimes one additional wire for battery negative.

Think of it as inputting the voltage of each group of cells and acting as a switch on the negative terminal of the battery for cutting off discharge and charge when the battery is out of balance.

That bike maybe had no original BMS because Li-Mn chemistry doesn't use balancing:

My understanding is that 'self balancing' is a poor term to characterize the Konion LiMn cells. It's more that balancing is not required, since it is a relatively safe and stable chemistry, and the charge efficiency dramatically decreases at higher SOC's so marginally weaker cells have time at the lower efficiency to 'catch up' towards the top of the charge. If you have one really weak cell, you will still likely have problems. Especially in smaller packs for drills, one weak cell tends to mean the end of the pack, so this isn't a big deal. On a larger pack, you can have a bad cell and not even know.
You know,
I’m sorry i forgot to include the pic of the “bms” although i think it just charges and monitors the temp because there were never any wires connecting to each of the cells.
Doesn't look tough to hook up. The pads are clearly labeled. E.g. +VBatt, -VBatt, MOT-, MOT+. There's also pictures online of it with original wiring:

Unfortunately, it's useless to you since it's designed for LiMn chemistry cells, not LiIon like your replacement battery:
BionX BMS SMC 5.2 for 37V Li-ion (10S) Smart Connect 5.2 and battery case only.

No cells!

Smart Connect 5.2 works only with manganese li-ion cells.

The electronics come from a 37V 7.2Ah battery and work perfectly.
Private sale, therefore no guarantee or return.
lnanek said:
Smart Connect 5.2 works only with manganese li-ion cells.
Aren't the specifications other than chemistry the same or close? How does the device recognize chemistry?
Sorry, I'm missing something...
See the first quote in my first reply for why LiMn is a safer chemistry that doesn't require balance wires.
I have rebuilt several of these batteries the following way:

I would advise using a 10S common port BMS for this rebuild..

Pin 2 of the charging port should currently (or did) have a thermistor that connected to -chrg on the factory board - remove this wire from the factory board and connect it to the P- on the new BMS. The original black VBATT- that went to the negative side of the pack wire will now also connect to the P- on the new BMS.

Pin 3 on the charger should be a yellow wire which is also contains a thermistor. This should be connected to the negative terminal of the new pack.

Pin 4 is red and connects to the positive side of the new pack.

B- on the new BMS connects to the main negative terminal on the new pack.

You will now have proper balancing and retain thermal protection (I also use BMS units with their own thermistor, too)

You cannot change ANYTHING on a BionX system, they where the Apple of the ebike world! Ask GRIN! They even modified the MOTORS so they could not be used by anything else then BionX controller! We have repaired a few batteries! First, if charging does not work, install a secondary BMS! We had to do that once! Second! The BMS remembers capacity! You will have to ride the ebike untill the battery dies a few times to recalibrate! Batteries made by BMZ Group, but doubt that helps! They are the foxconn of the eu ebike battery world! Good luck!
The Battery Doctor said:
They even modified the MOTORS so they could not be used by anything else then BionX controller!
You might want to look up the various threads using non-bionX external controllers on them before making such statements.