Harman/Kardon Onyx Studio 5 Compatible Battery 3.7V 3500mAh ID997

Harman/Kardon Onyx Studio 5 / Studio 6 — 3.7V Li-ion Replacement Battery (ID997 / IAA007NA)

This 3.7V, 3500mAh Li-ion cell fits the Harman/Kardon Onyx Studio 5 and Onyx Studio 6 portable Bluetooth speakers, including model codes HKOS6GRYSG and HKOS6BLKSG. It replaces OEM part numbers ID997 and IAA007NA. Swap it in when the original cell no longer holds a charge or the speaker shuts down mid-session.

• Studio 5 and Studio 6 shared platform: Both the Studio 5 and Studio 6 use the same 3.7V cell, connector pinout, and BMS handshake protocol, which is why one part number covers both units. The physical footprint — 76.50 × 19.50 × 19.50mm — matches the internal battery bay on each model without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Studio 5 platform. The BMS accepted the charge curve without fault codes, balanced correctly at top-of-charge, and applied the low-voltage cutoff at the expected threshold before the speaker could brown out the amplifier stage.
• Fuel gauge recalibration after install: After fitting a new cell, run the speaker down until it powers off on its own, then charge it uninterrupted to 100%. Skipping this step leaves the onboard fuel gauge reading from stale data, which causes the indicator to report incorrect charge levels — you'll see the battery icon jump or drop unexpectedly during playback.

Why the Onyx Studio 5 shuts down at high volume before the battery indicator reaches empty

At loud listening levels, the amplifier draws a sharp current spike that the aging or degraded cell cannot supply without a voltage sag. The BMS reads that sag as an under-voltage event and trips the protection circuit, cutting power to the speaker — even if the indicator still shows 30% or 40% remaining. A fresh cell with lower internal resistance sustains the current spike without sagging below the BMS trip threshold. If the new cell still causes shutdowns, check that the speaker firmware is current, as early Studio 5 units had BMS communication bugs patched in later releases.

Speaker won't respond to USB charging after sitting unused for months

When the cell self-discharges below roughly 2.5V during long storage, most USB-C power delivery controllers won't initiate a charge handshake — the cell voltage is too low to meet the PD minimum acceptance threshold. The speaker appears completely dead and shows no charging indicator. Apply a low-current pre-charge using a bench supply or a charger with a recovery mode to bring the cell above 3.0V, at which point normal USB-C charging resumes. If no recovery charger is available, replacing the cell is the practical next step.