Harman/Kardon Onyx Mini Replacement Battery 3.7V 3000mAh

Harman/Kardon Onyx Mini — 3.7V Li-Polymer Replacement Battery (CP-HK07)

This 3.7V, 3000mAh lithium-polymer cell replaces the original battery in the Harman/Kardon Onyx Mini portable Bluetooth speaker. It restores audio playback and Bluetooth connectivity when the factory cell has degraded and no longer holds adequate charge. Capacity is 11.1Wh, matching the original pack specification.

• Onyx Mini compatibility: The Onyx Mini uses a single-cell Li-Polymer pack at 3.7V nominal, managed by an onboard BMS that monitors cell voltage and controls charge cutoff. This replacement matches that voltage rail and connector orientation so the BMS handshake completes without errors.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Onyx Mini board. The BMS accepted the cell without fault flags, charge termination fired correctly at 4.2V, and the low-voltage cutoff triggered at the expected threshold before cell damage could occur.
• Monthly discharge cycle for the Onyx Mini: This speaker gets topped off constantly on desks and shelves. Let it drain below 20% at least once a month before recharging — constant top-off charging without a full discharge causes fuel gauge drift and accelerates capacity fade on the Li-Polymer cell.

Audio distorting before the battery indicator reaches empty on the Onyx Mini

The Onyx Mini's amplifier draws a sharp current spike at higher volume levels. As the cell ages and internal resistance rises, voltage sags under that combined amplifier and Bluetooth radio load. The voltage drop crosses the amplifier's minimum supply threshold before the battery indicator registers as empty, so the speaker clips and distorts while the gauge still shows charge remaining. A fresh cell with lower internal resistance sustains voltage under load and pushes that distortion point much further down the discharge curve.

Onyx Mini not waking from USB charge after sitting unused for weeks

Li-Polymer cells that sit discharged for extended periods drop below the USB-C PD minimum acceptance voltage — typically around 2.5V per cell. At that point, the speaker's charge circuit may not recognise the pack as chargeable and the device appears completely dead. Use a dedicated Li-Po charger set to a recovery or trickle mode to bring the cell voltage back above 3.0V first. Once the cell reads above 3.0V, plug into USB and normal charging will resume.