Amazon Echo 1st Gen Replacement Battery 3.7V 3350mAh

Amazon Echo Tap — 3.7V Li-ion Replacement Battery (58-000138)

This 3.7V, 3350mAh Li-ion cell replaces the original battery in the Amazon Echo Tap (PW3840, PW3840KL). It matches the OEM part number 58-000138 and fits the Tap's battery bay without modification. Capacity figure is taken directly from the product specification — 12.4Wh total energy.

• PW3840 and PW3840KL platform: Both model variants run the same 3.7V single-cell architecture with an identical connector and BMS handshake. One battery covers both, because Amazon used the same power rail and protection circuit across the full Tap production run.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Tap unit, confirmed BMS communication cleared without error flags, and verified the fuel gauge reported accurately across the full state-of-charge range.
• Fuel gauge calibration on the Tap: The Tap's onboard fuel gauge drifts when the cell is never allowed to discharge below 30%. Once a month, run the speaker down past the low-battery warning before plugging in — this lets the BMS recalibrate the full capacity window and keeps the indicator accurate.

Audio distorting before the battery indicator reaches empty on the Echo Tap

The Tap's amplifier draws a short, high-current spike each time bass frequencies hit. As the cell ages and internal resistance climbs, that spike causes a voltage sag the BMS cannot mask — the amp clips before the fuel gauge has caught up with actual cell state. You hear crackling or thinning audio while the indicator still shows two bars. A fresh cell with low internal resistance eliminates the sag and restores clean output. If distortion persists after fitting a new battery, check that the speaker grille is not blocked — thermal load on the amp compounds the issue.

Echo Tap not waking from USB after sitting unused for weeks

A Tap left uncharged for several weeks can drop below the minimum acceptance voltage the charging IC requires to initiate a charge cycle — typically under 2.5V for this cell chemistry. The device appears completely dead and does not respond to the USB cable. The fix is a trickle pre-charge: leave the USB cable connected for 20–30 minutes without expecting any screen or LED response, then check for the charging indicator. If the cell has self-discharged below 2.0V, the BMS may have latched into deep-discharge lockout and the cell will need replacement rather than recovery.