Sony NW-HD1 MP3 Player Replacement Battery 3.7V 800mAh

Sony NW-HD1 MP3 Player — 3.7V Li-Polymer Replacement Battery (PMPSYHD1)

This 3.7V 800mAh Li-Polymer battery replaces the original PMPSYHD1 cell in the Sony NW-HD1 HD Walkman. The NW-HD1 is a portable digital audio player from Sony's mid-2000s HD Walkman line. When the original cell degrades and no longer holds a usable charge, this replacement restores normal operation.

• NW-HD1 fitment: The NW-HD1 uses a slim Li-Polymer cell with a specific connector and BMS handshake tied to the device's charge circuit. This cell matches the OEM voltage, form factor (51.21 × 33.30 × 3.60mm), and connector orientation so the charge IC reads the pack correctly.
• Bench tested on actual hardware: We cycled this cell through the NW-HD1's charge circuit and confirmed the BMS communicated cleanly — no fault codes, no charge current rejection, and the device accepted a full charge from empty without interruption.
• First-charge protocol after cell swap: After installing, charge the NW-HD1 fully before powering it on. Media players of this era often enter a deep-discharge protection state after a cell swap, and the charge IC needs to push a slow trickle current before it accepts a normal charge rate.

Battery percentage jumping erratically after cell swap

The NW-HD1 uses a voltage-threshold method to estimate remaining charge — it does not have a fuel gauge IC that recalibrates automatically. After fitting a new cell, the device's charge indicator is reading a voltage curve it hasn't mapped yet. Run two or three full charge-to-empty cycles and the readings stabilise. If the display still jumps after three cycles, check that the connector is fully seated — a loose pin causes intermittent voltage spikes the indicator reads as charge swings.

Playback cuts out before the battery indicator shows empty

The NW-HD1's audio amplifier draws a short current spike to drive headphone output, and near the end of the cell's discharge curve — typically below 3.5V — the cell can no longer sustain that spike without voltage sagging below the device's cutoff threshold. The player shuts down to protect the cell even though the indicator shows charge remaining. This is a normal characteristic of aged or cold Li-Polymer cells. If it happens frequently, the cell may have aged past usable capacity — check open-circuit voltage after a full charge; a healthy cell should read 4.1–4.2V.