About this replacement
JBL PartyBox 310 — 7.4V Li-ion Replacement Battery (GSP-2S4P-PB350B)
This 7.4V 13400mAh Li-ion battery replaces the original GSP-2S4P-PB350B and GSP-2S4P-PB350A cells in the JBL PartyBox 310 portable Bluetooth speaker. It fits directly into the PartyBox 310's battery bay and connects to the onboard BMS without modification. Capacity is 13400mAh (99.16Wh), matching the original pack.
- PartyBox 310 fit: The 310 runs its Class D amplifier and Bluetooth radio off a single 7.4V 2S4P lithium pack. This battery replicates that cell configuration — same voltage rail, same connector pinout, same BMS handshake — so the speaker's fuel gauge reads correctly from the first charge.
- Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the PartyBox 310 and confirmed the BMS balanced both cell groups without error flags. The amplifier drew peak current under loud playback without triggering the low-voltage cutoff prematurely.
- PartyBox 310 discharge habit: The 310 often lives plugged in between events. Constant top-off charging without a full discharge causes fuel gauge drift on the 2S4P pack. Run the battery below 20% at least once a month before recharging to keep the cell-level capacity readings accurate.
Why the PartyBox 310 distorts audio before the battery indicator hits empty
At high volume, the Class D amplifier inside the 310 pulls large current spikes that cause voltage sag across the pack. If the cells have aged or been shallow-cycled, internal resistance rises — and the pack voltage drops below the amplifier's clean-headroom threshold before the fuel gauge registers low. The speaker clips the audio signal to protect the amp rather than shut down. Replacing the pack eliminates the high-resistance cells responsible for the sag.
PartyBox 310 won't wake from USB-C when battery is deeply discharged
If the 310 has sat unused for several months, the 2S4P cells can drop below the minimum acceptance voltage for USB-C Power Delivery negotiation — typically under 2.5V per cell. The charger handshake fails and the speaker appears completely dead. Connect the original JBL AC adapter rather than a USB-C PD charger and leave it for 20–30 minutes to allow the BMS to trickle-charge the cells back above the PD floor. Once the BMS accepts the charge, normal charging resumes and the speaker powers on.