Sharp GX-BT280 Replacement Battery 3.7V 5200mAh Li-ion

Sharp GX-BT280 / GX-BT290 — 3.7V Li-ion Replacement Battery (INR18650-1S2P)

This is a 3.7V, 5200mAh Li-ion replacement battery for the Sharp GX-BT280 and GX-BT290 portable Bluetooth speakers. It uses an INR18650 1S2P cell configuration — two 18650 cells in parallel — to match the original pack's voltage rail and capacity. When your speaker no longer holds a charge or cuts out early in a session, this is the cell pack that restores it.

• GX-BT280 and GX-BT290 compatibility: Both models share the same battery bay dimensions and draw from the same 3.7V nominal rail. The BMS handshake and connector pinout are identical across this pair, so one battery covers both units without any modification.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on the GX-BT290 platform. The BMS handled both the amplifier draw at high volume and the Bluetooth radio's combined current spike without tripping into protection mode. Capacity read 5200mAh at room temperature on a calibrated discharge cycle.
• Monthly discharge cycle on this speaker: The GX-BT280 is typically charged at a desk or bedside and rarely plays below 50%. Let the speaker run down past 20% at least once a month before recharging. Constant shallow top-off cycling causes fuel gauge drift and accelerates cell degradation faster than it would on a device with deeper, regular discharge patterns.

Why the GX-BT280 audio distorts before the battery indicator reads empty

As a Li-ion cell ages, its internal resistance rises. Under amplifier load, voltage sag pulls the cell below the threshold the amp needs to drive the speaker cleanly — even while the indicator still shows charge remaining. The result is clipping distortion that appears at moderate to high volume before any low-battery warning triggers. A fresh 5200mAh pack with low internal resistance eliminates the sag that causes this symptom. If distortion persists on a new battery, check that the charging port is clean and the cell is reaching a full 4.2V at end of charge.

Speaker wakes from USB but won't pass audio — deeply discharged pack

If the GX-BT280 sits unused for several weeks, the cell can self-discharge below the USB-C PD minimum acceptance voltage — typically around 2.5V per cell. At that point the charger may briefly show activity then stop, and the speaker appears dead rather than charging. Connect it to a 5V USB-A source rather than a PD charger; lower-voltage trickle input often re-initialises the BMS when a PD handshake is being refused. Once the cell climbs back above 3.0V, switch to your normal charger and complete a full charge to 4.2V before use.