JBL Charge 4 Replacement Battery 3.7V 7800mAh Li-ion ID998

JBL Charge 4 / Charge 4J — 3.7V Li-ion Replacement Battery (ID998)

This 3.7V, 7800mAh Li-ion cell replaces the original battery in the JBL Charge 4, Charge 4J, JBLCHARGE4BLUAM, and Charge 4BLK. It restores both wireless audio playback and the speaker's USB power-bank function. Capacity is rated at 28.86Wh — matching the original cell specification.

• Charge 4 series compatibility: All four Charge 4 variants — Charge 4, Charge 4J, JBLCHARGE4BLUAM, and Charge 4BLK — share the same battery bay dimensions (66.30 x 38.50 x 36.30mm), the same 3.7V cell voltage, and the same BMS connector pinout. The ID998 cell fits all four without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Charge 4 unit. The BMS accepted the cell immediately, balanced charge current correctly across stages, and the USB power-bank output activated at full charge without prompting a reset.
• Fuel gauge calibration after swap: After fitting this battery, run the speaker down until it powers off automatically — do not interrupt it. Then charge it uninterrupted to 100%. This lets the BMS re-learn the cell's actual capacity and stops the charge indicator from reading full when the cell is only at 60–70%.

Capacity fade from constant top-off charging on the Charge 4

The Charge 4 is often left plugged in on a desk between uses. Li-ion cells held at 100% charge under trickle current degrade faster than cells that cycle between 20% and 80%. The BMS cannot prevent this — it only stops overcharge, not prolonged float voltage stress. If the original battery lost capacity quickly, the charging habit is usually the cause. With a replacement cell, occasional full discharge cycles slow that fade significantly.

USB power-bank output not waking up on a deeply discharged pack

The Charge 4's USB-A output port requires the cell to sit above approximately 3.0V before the boost converter activates. A deeply discharged pack — one left unused for several months — can drop below that threshold and appear completely dead. Plug the speaker into its own charger via USB-C and leave it for at least 20–30 minutes before testing the USB output port. The BMS uses a low-current pre-charge phase to bring the cell back above the minimum acceptance voltage before resuming normal charge rate.