JBL PartyBox Club 320 Replacement Battery 7.4V 10000mAh

JBL PartyBox Club 320 / Stage 320 / Xtreme 4 — 7.4V Li-ion Replacement Battery (FG4CELL21700G)

This is a 7.4V 10000mAh (74Wh) Li-ion replacement battery for the JBL PartyBox Club 320, PartyBox Stage 320, and Xtreme 4 portable speakers. It replaces OEM part numbers FG4CELL21700G and FG4CELL21700H. When the original cell degrades and the speaker cuts out early or refuses to charge, this swap restores full electrical capacity to the audio system and internal amplifier.

• PartyBox Club 320, Stage 320, and Xtreme 4 compatibility: These three models share the same 7.4V battery rail, physical cell format, and BMS connector pinout. One battery covers all three because the amplifier board and power management circuit draw from the same voltage reference across the range.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the PartyBox platform and confirmed the BMS handshake completed without fault codes — cell balancing and over-discharge cutoff both triggered at expected thresholds.
• Monthly discharge cycle for PartyBox speakers: Let the speaker play down below 20% at least once a month before recharging. These speakers are frequently topped off mid-session without a full discharge, which causes the fuel gauge to drift — the indicator reports full while usable capacity has already dropped.

Audio distorting before the battery indicator reaches empty

The PartyBox amplifier draws high instantaneous current at loud volumes. As cell voltage sags under combined amplifier and Bluetooth radio load, the amp hits its minimum supply threshold before the fuel gauge shows empty. The result is audible clipping and distortion — not a speaker fault, but a voltage floor problem. A cell below about 6.8V under load will trigger this; a fresh 7.4V cell eliminates it.

USB-C charging not starting on a deeply discharged pack

If the PartyBox Club 320 has sat unused for months and the cell has self-discharged below the USB-C PD minimum acceptance voltage, the charger handshake never completes and the indicator stays dark. The BMS blocks inbound current to protect a cell it reads as critically low. Connect the speaker to a USB-C charger and leave it for 15–20 minutes — the BMS trickle-charges the cell back above the acceptance threshold before switching to normal charge current. If nothing happens after 30 minutes, the original cell is likely at or below recovery voltage, which is the point where a replacement cell is the only path forward.