About this replacement
JBL PartyBox Club 120 / Encore 2 — 5.4V HPC Replacement Battery (FG2CELL21700P)
This is the FG2CELL21700P replacement battery for the JBL PartyBox Club 120 and PartyBox Encore 2 portable speakers. It runs at 5.4V with a 4500F (24.3Wh) capacity, matching the original cell specification. It restores wireless operation when the factory pack has degraded or failed entirely.
- PartyBox Club 120 and Encore 2 compatibility: Both models share the same 5.4V HPC cell format, connector pinout, and BMS handshake protocol — that is why one part number covers both. Swap in either unit without modification.
- Bench tested on actual hardware: We cycled this pack through repeated charge and discharge sequences on the PartyBox platform. The BMS accepted the cell, reported state-of-charge accurately to the speaker's indicator LEDs, and held voltage steady under combined amplifier and Bluetooth radio draw.
- Monthly discharge cycle for PartyBox users: If the speaker sits on a shelf or desk and gets topped off before dropping below 50%, run it down past 20% at least once a month before recharging. Constant shallow cycling causes fuel gauge drift and accelerates capacity fade on this cell chemistry.
Audio distortion before the battery indicator reaches empty on the PartyBox Club 120
The PartyBox Club 120 amplifier draws a sharp current spike at high volume. When the cell ages and internal resistance rises, voltage sags under that spike even though the indicator still shows charge remaining. The amplifier clips because rail voltage has dropped below its operating floor, not because the pack is actually empty. Replacing the cell restores the voltage headroom the amplifier needs and pushes that clipping point back to where it belongs — near actual depletion.
Speaker won't wake from USB-C after sitting unused for several weeks
HPC cells that have self-discharged below the USB-C Power Delivery minimum acceptance threshold will not trigger the PD handshake. The charger sees no valid negotiation response and supplies nothing, so the pack stays dead. Connect the speaker to a 5V 1A USB-A source instead — this bypasses PD negotiation and trickle-charges the cell back above the threshold. Once the indicator shows at least one LED, switch back to the USB-C charger and complete a full charge cycle.