Harman/Kardon Esquire 2 Compatible Battery CP-HK03 3.7V 3500mAh

Harman/Kardon Esquire 2 — 3.7V Li-Polymer Replacement Battery (CP-HK03)

This 3.7V 3500mAh Li-Polymer cell replaces the original pack in the Harman/Kardon Esquire 2 portable Bluetooth speaker. It matches the OEM part numbers CP-HK03 and GSP805070 and fits the speaker's internal battery bay without modification. Capacity figures are taken directly from product data — 3500mAh / 12.95Wh.

• Esquire 2 fitment: The Esquire 2 runs a single Li-Polymer cell at 3.7V nominal, feeding both the Class D amplifier and Bluetooth radio from one shared power rail. This cell matches the OEM footprint (71.00 x 49.50 x 7.80mm), connector pinout, and BMS handshake so the speaker's fuel gauge reads correctly on first boot.
• Bench tested on actual hardware: We cycled this cell through charge and load discharge on the Esquire 2 platform, confirming BMS protection thresholds — overvoltage cutoff at 4.2V and undervoltage cutoff before the cell drops below 3.0V under combined amplifier and radio draw at high volume.
• Fuel gauge calibration tip: Once a month, let the Esquire 2 play until it powers off on its own before recharging. Constant top-off charging from 60–80% without ever reaching a full discharge causes the fuel gauge IC to drift, making the battery indicator unreliable and accelerating capacity fade on the Li-Polymer cell.

Why the Esquire 2 audio cuts out before the battery indicator hits empty

The Esquire 2 drives a Class D amplifier and a Bluetooth radio from the same 3.7V cell. At high volume, the combined current draw causes the cell voltage to sag below what the amplifier needs to operate cleanly, even when the fuel gauge still shows charge remaining. The BMS reads this voltage sag as an undervoltage event and shuts the output rail before the indicator reaches zero. A fresh cell with lower internal resistance holds voltage under load and eliminates these premature cutoffs.

Esquire 2 won't wake from USB charging after battery fully drained

If the Esquire 2 sits discharged for several weeks, the Li-Polymer cell can drop below the USB-C PD minimum acceptance voltage — typically around 2.5V — and the charging IC refuses to begin a normal charge cycle. Plug in the USB-C cable and leave it connected for at least 20–30 minutes without pressing any buttons; the charger will deliver a low-current trickle to recover the cell voltage before switching to full charge rate. If the LED shows no activity after 45 minutes, the original cell has failed and replacement is required. After fitting this cell, the speaker will wake normally from USB on first connection.