e-bikes and battery questions

Hello fellows,

More or less recently my brother, owner of some sort of “Surak” Biwbik branded e-bike, asked me about overhauling one of its batteries with newer, higher capacity cells.

After taking a look at the battery, I backed out. The connector of the battery remembered me of laptop batteries, SMBus and having to deal with @#$% propietary electronics. In a laptop battery, basically you need to reset its closed source microcontroller software or take a lot of care to avoid the stuff deeming the battery @#$%ed up while you overhaul it (if the software still considers it in good shape to start with, of course). Without reprogramming tools and knowledge or brand new BMSs that basically is between a pain in the arse and a nightmare. :|

Investigating the thing some more, made a search for e-bike mid drive systems in AliExpress and took a look at this descriptive advertisement:

This is more in line with my idea of a self-managed system, with battery packs connected with a standard two pin power connector using standard BMS systems. :???:

I think I've sort of given myself an answer, I just have to ask my brother if that e-bike he bought can use a standard battery pack.

What is your experience with e-bikes and their battery packs? As I see this stuff the DIY idea looks much better, allowing me flexibility to choose battery pack chemistry, size, probably adding some extra in series stage to the battery to slightly increase power (V² proportional)…

It’s been a while since I’ve researched e-bikes, but from what I remember, most use some form of 18650 cells in the pack. The one I own is a 36V setup to power a 250W motor. Less powerful hub motor, but it can fold to a very compact size. Given that, the below might be terribly outdated:

The basics I remember are most DIY packs range from 12-14s configuration for 36-52V setups. The more voltage, the less amps needed to drive the motor and less strain/heat on the control system. BMS for the pack is setup pretty much the same, main charge leads and balancing leads, etc. The DIY route definitely allows for more flexibility, but also requires good soldering/spot welding setup to make the needed pack. If there’s a change in voltage/series setup, then make sure your drive control board is made for it.

As far as I know, most bikes (maybe including your brother’s) runs on a plain pack plus a BMS, without any proprietary boards to control it. Any fancy monitoring features like Bluetooth usually resides on the drive control board that ties in the throttle, pedal assist, regenerative coasting, speedometer and other features. If there are more than two pins on the existing pack, it may be to support battery monitoring and regenerative coasting features. There’s no way to know for sure unless the existing pack is torn apart.

I think you may be better off posting at EndlessSphere or another EV forum.