About this replacement
Harman/Kardon Onyx Studio 7 — 3.7V Li-ion Replacement Battery (GSP-1S1P-OS7A)
This is a 3.7V, 3350mAh Li-ion cell replacement for the Harman/Kardon Onyx Studio 7 Bluetooth speaker. It fits the Onyx Studio 7 only — not earlier Studio models. Capacity is 3350mAh (12.4Wh), matching the original cell specification.
- Onyx Studio 7 fitment: The Studio 7 uses a single-cell Li-ion pack with a proprietary connector and a fuel gauge IC that reads state-of-charge from the cell's voltage curve. A replacement cell must match the 3.7V nominal voltage and report the correct capacity range, or the indicator ring will misread from the first charge cycle.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Studio 7 mainboard. The BMS accepted the pack without fault codes, the fuel gauge calibrated correctly, and the amplifier drew cleanly through high-volume bursts without triggering undervoltage protection.
- Fuel gauge maintenance for daily use: The Onyx Studio 7 sits on desks and gets topped off constantly. Charge to 100%, then let it discharge below 20% at least once a month before plugging back in. Skipping this causes the fuel gauge IC to drift, so the speaker shuts off at what it reports as 30% charge.
Audio distortion before the battery indicator reaches empty on the Studio 7
The Studio 7 amplifier pulls a short, high-current spike on loud transients — bass hits and drum attacks in particular. When the cell's internal resistance rises with age, that spike causes a voltage sag below 3.2V, which the amplifier reads as low supply and clips the output. The battery indicator can still show two bars when this starts happening. A fresh cell with lower internal resistance eliminates the sag and stops the clipping at the source.
Studio 7 not waking from USB-C after the battery fully drained
If the Studio 7 discharges completely and sits for several days, the cell voltage can fall below 2.5V. At that level, the USB-C PD controller will not negotiate a charging contract — the port looks dead and nothing happens when you plug in. To recover, use a charger that outputs a constant 5V without PD negotiation, leave it connected for at least 20 minutes, and the BMS pre-charge circuit will trickle current into the cell until it crosses 2.9V and normal charging resumes.