About this replacement
Amazon Tap — 3.7V Li-ion Replacement Battery (58-000138)
This 3.7V 2600mAh Li-ion cell replaces the original battery in the Amazon Tap portable Bluetooth speaker. It fits models PW3840 and PW3840KL. Swap it when the original pack no longer holds charge or the speaker stops working away from a power source.
- PW3840 and PW3840KL compatibility: Both model variants use the same 3.7V single-cell architecture and the same connector pinout. The BMS handshake on each accepts this cell without remap or firmware change.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Tap unit. The BMS accepted charge immediately, balanced the cell correctly, and cutoff triggered cleanly at the low-voltage threshold without tripping a fault state.
- Tap-specific charge habit: The Amazon Tap sits on its charging cradle between uses, which means it rarely discharges past 80%. Let the battery drain below 20% at least once a month before recharging — this corrects fuel-gauge drift that builds up from constant shallow top-off cycles on this speaker's Li-ion cell.
Why the Tap runs warm in its fabric housing during extended play
The Tap's cylindrical fabric shell traps heat from two sources at once: the amplifier dissipating power during audio output and the Li-ion cell generating heat during discharge. At high volume, amplifier draw spikes and battery discharge rate rises together. The housing has no active ventilation, so heat accumulates rather than dispersing. If the unit feels hot to the touch, drop the volume and let it rest — sustained heat above 40°C accelerates cell degradation faster than normal cycling.
Audio distorting before the battery indicator reaches empty
This happens when the cell voltage sags under combined amplifier and Bluetooth radio draw before the fuel gauge hits zero. A Li-ion cell at moderate state-of-charge can still show 20–30% on the indicator while actual terminal voltage drops below the amplifier's clean operating threshold under load. The result is clipping distortion in the audio output — not a speaker fault. Check the Tap's charge state under load: if resting voltage reads above 3.5V but distortion appears at high volume, the cell has degraded and can no longer sustain the current spike. Replace the cell and verify resting voltage sits at or above 4.1V after a full charge.