Harman/Kardon Onyx Studio 3 Replacement Battery CP-HK02 3.7V

Harman/Kardon Onyx Studio 3 — 3.7V Li-ion Replacement Battery (CP-HK02)

This is a 3.7V, 3200mAh Li-ion replacement cell for the Harman/Kardon Onyx Studio 3 portable Bluetooth speaker. It slots in as a direct swap for part number CP-HK02 when the original cell can no longer hold charge or fails to power the unit. Capacity is 11.84Wh, matching the original specification.

• Onyx Studio 3 fit: The CP-HK02 cell is specific to the Studio 3 housing and its internal connector arrangement. The BMS on this speaker communicates charge state to the LED indicator ring — a mismatched cell will report incorrect charge levels or refuse to charge at all.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Studio 3 board. The BMS accepted the cell without fault codes, the LED ring reported charge state accurately, and audio output held steady through the draw cycle.
• Fuel gauge maintenance on the Studio 3: This speaker is typically kept plugged in on a desk between uses. Constant top-off charging without a full discharge causes fuel gauge drift over time — the indicator ring shows full while actual capacity has already dropped. Discharge below 20% at least once a month before recharging to keep the gauge calibrated.

Audio distorting before the battery indicator reaches empty on the Studio 3

The Onyx Studio 3 amplifier draws a sharp current spike at higher volume levels. When the cell voltage sags under that combined amplifier and Bluetooth radio load, the amp clips before the battery indicator has reached its low-battery threshold. The speaker sounds distorted or compressed, but the LED ring still shows one or two bars remaining. This is not a speaker fault — it is voltage sag on a degraded or deeply discharged cell. A fresh cell at full charge holds voltage through those peaks and eliminates the distortion.

Studio 3 not responding to USB charge after sitting unused for months

Li-ion cells that sit discharged for extended periods drop below the minimum acceptance voltage the charging circuit needs to begin a charge cycle — typically around 2.5V for this cell chemistry. When this happens, the Studio 3 shows no charging indication and appears completely dead. Some units will recover with a slow pre-charge trickle if the charger supports it, but cells that have dropped below 2.0V rarely recover to usable capacity. If the speaker shows no response after 30 minutes on a known-good 5V USB source, the cell needs replacement rather than continued charging attempts.