Harman/Kardon One Replacement Battery 3.7V 1800mAh

Harman/Kardon One — 3.7V Li-Polymer Replacement Battery (CP-HK05)

This 3.7V, 1800mAh Li-Polymer battery replaces the original CP-HK05 / PR-652954 cell inside the Harman/Kardon One portable Bluetooth speaker. It fits the One speaker housing directly, restoring power to a unit that no longer holds a usable charge. Capacity is 6.66Wh, matching the original specification.

• Harman/Kardon One fit: The One uses a slim Li-Polymer pouch cell at 55.00 × 32.10 × 10.60mm. That specific footprint and the 3.7V nominal rail are fixed by the speaker's internal PCM, so only a cell matching both dimensions and voltage will clear the protection circuit correctly.
• Bench tested on actual hardware: We cycled this cell through the One's charge controller and confirmed the PCM trips at the correct low-voltage cutoff without locking out the USB charge circuit. Charge termination at the top end also held within spec.
• Fuel gauge reset after swap: After fitting a new cell, run the speaker down until it powers off on its own, then charge it uninterrupted to full. The One's onboard fuel gauge recalibrates its empty and full reference points on that first full cycle — skipping this step causes the indicator to misread state of charge from day one.

Why the Harman/Kardon One cuts out at high volume even on a charged battery

At peak volume, the One's amplifier draws a sharp burst of current on top of the Bluetooth radio's steady draw. A degraded or partially discharged Li-Polymer cell cannot sustain that combined spike without its terminal voltage dipping below the PCM's cutoff threshold. The protection circuit reads that dip as an unsafe low-voltage event and shuts the cell down — even if the indicator shows 40–60% remaining. A fresh cell at full charge holds terminal voltage above 3.5V under that combined load and keeps the PCM from tripping.

Audio distorting before the battery indicator reaches empty

If you hear crackling or clipping while the charge indicator still shows bars, voltage sag is usually the cause. As a Li-Polymer cell ages, its internal resistance rises — voltage drops under load faster than the indicator expects. The amplifier clips when it can't get enough voltage to complete the audio waveform, producing audible distortion. Check terminal voltage under load with a multimeter: if it falls below 3.3V while the speaker is playing at moderate volume, the cell has aged past its usable capacity and replacement is the fix.