Bose SoundLink Flex 83289 Replacement Battery 3.7V 3400mAh

Bose SoundLink Flex — 3.7V Li-ion Replacement Battery (83289)

This is a 3.7V, 3400mAh (12.58Wh) Li-ion replacement battery for the Bose SoundLink Flex portable Bluetooth speaker. It replaces OEM part number 83289. Fit this battery when the original cell no longer holds a charge or the speaker shuts down unexpectedly during playback.

• SoundLink Flex platform fit: The SoundLink Flex uses a single-cell Li-ion pack at 3.7V nominal, matched to its onboard charging and protection circuit. This replacement cell matches that voltage rail and physical connector, so the BMS handshake completes without error flags on the speaker's firmware.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the SoundLink Flex platform. The BMS accepted the pack immediately, charge termination triggered correctly at 4.2V, and low-voltage cutoff engaged at the expected threshold without forcing a hard shutdown during audio output.
• Fuel gauge reset after install: After fitting a new cell, the SoundLink Flex's fuel gauge may read inaccurately for the first few cycles. Run the speaker down to the low-battery warning before recharging — do this for the first two full cycles to let the coulomb counter recalibrate against the actual cell capacity.

Capacity fade from constant top-off charging on the SoundLink Flex

Most SoundLink Flex users plug the speaker in at a desk whenever it drops below full. That habit keeps the cell sitting at 4.2V for long periods, which accelerates lithium plating on the anode and reduces usable capacity over time. The original 3400mAh cell can drop to effective capacity well under 2000mAh within 18 months under this pattern. Once per month, let the speaker play down past the low-battery indicator before recharging — this breaks the shallow-cycle pattern that kills the cell early.

SoundLink Flex won't wake from USB-C after sitting discharged for weeks

If the speaker is stored without charging, the Li-ion cell can drop below the USB-C Power Delivery minimum acceptance voltage — typically under 2.5V per cell. At that level, the PD controller in the speaker won't negotiate a charging contract and the speaker appears completely dead. Connect the USB-C cable and leave it for 15–20 minutes without pressing any button — some chargers will trickle current into a deeply discharged cell before PD negotiation starts. If the cell has dropped below 2.0V, recovery is not always possible and the cell needs replacement. Check for a faint LED pulse after that wait period as confirmation the pack is accepting charge.