Are active cell balancers a good alternative to a BMS?

In short - NO!

Why not?
Mainly one reason:

1. they usually have no way of stopping the charging process leaving you still exposed to all the potential risks of running BMS-less. So you only get a small part of the critical features a BMS should include

Other things to consider:

  1. active balancers are always on and always balance - but balancing during high discharge situations (aka riding your Onewheel) may not always be a good idea, but I guess opinions on this topic differ

  2. balancing is not as critical as you think it is - good quality cells do not need much balancing. I’ve personally never had to balance my Samsung 25R based pack (12s2p, 2 years now) and my Molicel p26a pack (18s2p, 6 months)

  3. how do you verify that your active balancer is working? Your battery is hidden in a box and all you ever see is total voltage

What are the key features a charge-only BMS will provide on top of balancing?

  • It acts as a fuse between charger and battery
  • It will stop the charging process if anything out of the ordinary happens, like bad cells, overvoltage, temperature, out-of-balance beyond threshold, etc
  • It protects the battery from a bad/wrong charger

If it’s a smart BMS it will also allow reporting cell voltages and temperatures

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Posting this for reference (not that it really matters because of the one and only point #1 above)

Testing active balancer - results - How-Tos & Esk8 mechanics - esk8.news: DIY Electric Skateboard Forums

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