Credit: Tom Zartler

ONYX 41AH Battery Unbalanced Fix

All ONYX 41Ah batteries have automatic balancing that activates at 80 volts or higher, regardless of the charger used. In the HD and EK versions, unbalancing often results from charging habits-mainly not spending enough time above the “start voltage” for proper balancing.

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Balance Delta

  • 0.300V – 0.500V = Needs attention
  • 0.030V – 0.002V = Healthy range

Balance Fix Instructions

For an unbalanced ONYX 41Ah battery, you can follow these steps: temporarily lower the “start voltage” and disable “balance only when charging.” This allows the battery to begin balancing at 74 volts or higher when unplugged from the charger-helping correct imbalances and improve long-term health.

In most cases, these settings are only temporary. However, in some instances, they may need to be permanent. If your ONYX 41Ah becomes unbalanced again after a few months, you can revert to these settings long-term-they may simply be a better fit for your charging habits.

  • Download and install the Overkill Solar BMS app.
  • Open the app within 5 feet of your battery.
  • Connect to your Onyx 41Ah battery by selecting the Bluetooth name that starts with HD or EK on the devices page.
  • Tap Settings at the bottom of the app.
  • Tap BMS Read in the top left corner.
  • Update the settings as follows:
  • Start Voltage: Change to 3700.
  • Bal. Only When Charging: Toggle OFF (grey, not yellow).
  • Tap BMS Write to save the changes.

Charge the Battery

  • Charge the battery to between 80V and 83V.
  • If the Balance Delta is:
  • 0.300V - 0.500V: Let the battery rest for 3 days without use to allow balancing.
  • Above 0.500V: Make a post in ONYX AF for assistance.

Monitor Progress

  • After 3 days, check the Balance Delta:
  • If it reduces to 0.030V, revert the settings to stock:
  • Start Voltage: 3900
  • Bal. Only When Charging: ON (green).
  • If the delta is still above 0.030V, continue to monitor daily. Ensure it’s decreasing.
  • If the delta increases, stop and post in ONYX AF.

Monitor Temperature

  • Ensure the battery temperature stays below 35°C (95°F).
  • If it exceeds this threshold, stop immediately and post in ONYX AF.

Balancing Checklist

  • Connect to the battery using the Overkill Solar BMS app.
  • Select the Bluetooth device name starting with HD or EK.

Change BMS Settings

  • Start Voltage: Set to 3700.
  • Bal. Only When Charging: Turn OFF (grey).
  • Save the changes with BMS Write.

Charge and Monitor Balance Delta

  • Charge to 80V - 83V.
  • Monitor the balance delta:
  • 0.300V - 0.500V: Rest the battery for 3 days.
  • Above 0.500V: Seek help in ONYX AF.

Check After 3 Days

  • If the delta reduces to 0.030V or lower, revert settings to stock:
  • Start Voltage: 3900.
  • Bal. Only When Charging: ON (green).
  • If still unbalanced, monitor daily.

Watch Temperature

  • Ensure temperatures stay below 35°C (95°F).

Balanced Unchanged

If your ONYX 41Ah battery’s balance delta is still sitting at 0.150V or higher after three days, continue balancing it for up to 10 more days. If the delta still doesn’t drop closer to 0.020V, your battery may be experiencing a memory effect. Follow these steps to try and break it and help restore proper cell balancing:

Memory Effect Reset Procedure

  • Discharge the battery as close to empty as possible, around 64V down to 60V.

  • Charge the battery fully to 80V or higher.

  • Maintain a full charge: Keep the battery balancing and every other day make sure it’s topped back up to at least 80V.

  • This process introduces a deep discharge followed by consistent full charges to help disrupt any memory effect and improve the balance delta.

If after 15 days there’s still no noticeable improvement, move to the next diagnostic step.

Analyze Cell Behavior Under Load

  • Open the BMS app and go to the screen showing cell groups 1–20.

  • Turn on the bike and start a screen recording on your phone.

  • Perform light, medium, and hard throttle pulls to capture how the cells respond under load.

  • Share the video recording with me so I can help analyze if any specific cell group is sagging abnormally or showing early signs of failure.

This will help determine if a particular group is physically degrading and contributing to the imbalance or causing performance issues.

Battery Repair

You can reach out to a battery repair service like North East Battery Systems-they can individually charge the cell groups to help bring them back into balance. While that’s not a guaranteed fix, I highly recommend consulting with them.

Battery Disposal

Contact your local Department of Sanitation for instructions on how to properly dispose of bike batteries at designated facilities in your area.