JBL PartyBox 310 Compatible Battery 7.4V 10400mAh GSP-2S4P

JBL PartyBox 310 — 7.4V Li-ion Replacement Battery (GSP-2S4P-PB350B)

This is a 7.4V, 10400mAh (76.96Wh) Li-ion replacement battery for the JBL PartyBox 310 portable Bluetooth speaker. It slots into the same battery bay as the factory pack and runs the amplifier, Bluetooth radio, and control board from a single cell group. If your PartyBox 310 no longer holds a charge or shuts down mid-session, this pack restores it to full working order.

• PartyBox 310 fit: The 310 uses a 2S4P Li-ion configuration to hit the 7.4V nominal rail the Class D amplifier board requires. The connector pinout and BMS handshake match the OEM pack — the speaker's charge controller will recognise the new battery without recalibration.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on a PartyBox 310 board, monitoring cell voltage balance across both series groups. The BMS held cutoff at the correct low-voltage threshold and balanced within 20mV across the 4P cell groups.
• Monthly discharge cycle for the PartyBox 310: This speaker typically lives plugged in at home between events. Running it down below 20% at least once a month before recharging keeps the fuel gauge calibrated and slows capacity fade — constant top-off charging without a full discharge accelerates cell degradation on the 2S Li-ion pack.

Why the PartyBox 310 amplifier clips before the battery indicator hits empty

The PartyBox 310 runs a high-current Class D amplifier that draws heavy bursts of current at loud volumes. As the battery ages and internal resistance rises, cell voltage sags under those current spikes even when the state-of-charge indicator still reads 20–30%. The amplifier hits its minimum operating voltage before the BMS trips the low-voltage cutoff, causing audible clipping and distortion. A new pack with low internal resistance restores the headroom the amplifier needs — the clipping symptom disappears at rated cell voltage above 3.5V per cell.

PartyBox 310 won't wake from USB-C after sitting unused for weeks

If the speaker sits stored for several weeks with a depleted battery, the cells can drop below the USB-C Power Delivery minimum acceptance voltage — typically below 2.5V per cell on the 2S pack. At that point the charger handshake fails and the unit appears completely dead. Connect the original JBL AC adapter rather than a USB-C PD charger, leave it for 30–45 minutes without pressing power, and the BMS pre-charge circuit will trickle the cells back above the 3.0V per cell threshold before resuming normal charge.