Soundcast VG3 Replacement Battery 3.7V 6800mAh Li-ion

Soundcast VG3 — 3.7V Li-ion Replacement Battery (2-540-009-01)

This is a 3.7V 6800mAh Li-ion replacement battery for the Soundcast VG3 portable Bluetooth speaker. It also fits the SUD-VGBT03A and 21391-VGBT03A units. Swap it when the original cell no longer holds a useful charge.

• VG3, SUD-VGBT03A, and 21391-VGBT03A compatibility: All three model codes share the same single-cell 3.7V architecture, connector pinout, and BMS handshake — the same replacement cell serves all of them without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the VG3 platform. The onboard BMS accepted the cell without fault flags, balanced correctly, and the speaker's fuel gauge tracked the state of charge through the full cycle.
• Monthly discharge cycle on the VG3: Soundcast VG3 users tend to top off the speaker after every short session. Constant shallow cycling without a full discharge causes fuel gauge drift and accelerates capacity fade on the Li-ion cell. Let the charge drop below 20% at least once a month before plugging back in.

Audio distorting before the battery indicator reaches empty

As the cell ages, internal resistance rises. Under the combined current draw of the amplifier and the Bluetooth radio, terminal voltage sags faster than the fuel gauge can reflect. The amplifier clips before the indicator shows low battery — you hear distortion while the display still shows charge. A fresh cell at 6800mAh and lower internal resistance eliminates the sag that causes clipping.

Bluetooth dropping specifically at high volume

Cranking the VG3 to maximum volume spikes amplifier current draw sharply. On a degraded or partially discharged cell, that spike pulls terminal voltage below the threshold the Bluetooth radio needs to stay connected. The radio drops out even though audio was fine at lower levels. If the dropout only happens above 70% volume, voltage sag under peak amp draw is the cause — a new cell resolves it.