Short version: that error is the Avinox system detecting a
conflicting communication signal on the battery bus, and your parallel external pack is almost certainly the cause — not a coincidence that it only happens with the extender connected.
Here's the mechanism, and why 70-80% is the telltale:
Avinox batteries aren't dumb cells — they talk to the motor. The main pack carries a BMS communication line alongside the 36V power, and the M2 expects exactly one authoritative voice on that bus.
@Astro66 spelled this out clearly: to parallel a second battery into an Avinox system you have to
isolate the second battery's communication entirely and only bridge the positive and negative 36V power connections —
→ view post. If the second pack is an Avinox unit, its comms line fights the main one and you get exactly the kind of fault code you're seeing.
And officially, this is a known dead end:
@Amflow_Support confirmed the Avinox battery hardware and firmware
do not support third-party battery extenders —
→ view post. So the system isn't malfunctioning so much as doing exactly what it was designed to do when it sees something it doesn't trust.
Why it triggers at 70-80%: that's the giveaway. As the two packs drain, their voltages diverge and the cell-balancing/charge-transfer current between them rises.
@Ndanger flagged this risk directly — a voltage mismatch between parallel packs means one battery dumps current into the other at potentially high rates, which the BMS reads as an abnormal condition and throws the comms/protection fault, shutting the motor down —
→ view post. The 70-80% window is just where your two packs reach the divergence threshold the BMS won't tolerate.
What I'd do:
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If the external pack is a second Avinox battery — stop. Its comms line will always conflict. That's the conflict the error is naming.
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The parallel connection must be power-only (P+ and P− at 36V), with the extender's communication completely isolated, per Astro66's method. If yours is bridging anything beyond the two power pins, that's your fault source.
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Match state-of-charge before connecting to keep the inter-pack current low — though honestly, on a system Amflow says doesn't support extenders, you're engineering around the manufacturer rather than with it.
Worth saying plainly: there's real cell/BMS damage risk in prolonged high-current transfer between mismatched packs, so I wouldn't keep riding through that error.
What's the external pack — a second Avinox battery, or a generic 36V cell? That changes the safe options a lot, so shout and I'll narrow it down.
