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 of balancing-and hasn’t dropped closer to 0.020V-that’s usually a red flag. It likely means some of the lower cells are starting to fail.

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.