JBL ROCK Replacement Battery GSP552035 3.7V 620mAh Li-Po

JBL ROCK — 3.7V Li-Polymer Replacement Battery (GSP552035 2S)

This is a 3.7V, 620mAh Li-Polymer replacement battery for the JBL ROCK portable Bluetooth speaker. It replaces the original GSP552035 2S cell when the pack no longer holds a charge or the speaker shuts down during playback. Capacity is 2.29Wh — matched to the original specification.

• JBL ROCK platform fit: The ROCK uses a compact 36.20 × 20.55 × 5.20mm pouch cell wired directly into the speaker's charge management IC. This replacement matches those physical dimensions and the 3.7V nominal rail the amplifier and Bluetooth radio share. A mismatch in cell size or voltage causes the BMS to reject the pack at first charge.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the ROCK platform. The BMS accepted the pack at first connection, balanced to full charge without flagging a fault, and held voltage steady through both Bluetooth pairing and sustained audio output.
• Monthly discharge cycle on a desk speaker: The ROCK often sits plugged in or topped off before it drops below 50%. Let the battery run below 20% at least once a month before recharging. Constant shallow cycling causes fuel gauge drift — the speaker reports full charge but actual capacity is significantly lower.

Bluetooth dropping at high volume on the JBL ROCK

At maximum volume, the ROCK's amplifier and Bluetooth radio draw current simultaneously. A degraded or low-capacity cell cannot sustain voltage under that combined load. Voltage sags below the radio's minimum operating threshold and the Bluetooth stack drops the connection to protect the circuit. Replacing the cell resolves the sag — the GSP552035 2S is rated to hold above 3.5V under this combined draw.

Audio distorting before the battery indicator reaches empty

If the ROCK's audio clips or distorts while the indicator still shows charge remaining, the cell voltage is sagging under amplifier load before the fuel gauge catches up. This happens when the cell has lost internal capacity but the gauge still reads the old baseline. The amplifier clips because it is not receiving enough voltage to drive clean output — it is not a speaker fault. Fit the new cell and run one full discharge cycle to let the gauge recalibrate to the actual 620mAh capacity.