Sony NWZ-ZX1 Walkman Replacement Battery 3.7V 1000mAh

Sony NWZ-ZX1 / MDR-HW700DS — 3.7V Li-Polymer Replacement Battery (US453759)

This is a 3.7V, 1000mAh Li-Polymer cell built to the US453759 specification. It fits the Sony NWZ-ZX1 high-resolution audio player and the MDR-HW700DS wireless headphone system. Swap it in when the original cell no longer holds a usable charge between sessions.

• NWZ-ZX1 and MDR-HW700DS compatibility: Both devices share the US453759 footprint — same 3.7V nominal rail, same connector orientation, and same BMS handshake protocol. The cell dimensions are 60.50 × 36.20 × 4.50mm, so it seats flat without pressure on the chassis.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a NWZ-ZX1 unit. The BMS accepted the cell immediately, balanced correctly to 4.2V at full charge, and the protection circuit tripped cleanly at the low-voltage cutoff without forcing the device into an unrecoverable state.
• First-charge protocol after installation: If the player sat unused for months before this swap, connect it to the Sony charger and leave it for 30 minutes before attempting to power on. Extended storage can push the cell into deep-discharge protection, where the device draws trickle current before it accepts a full charge cycle.

Battery percentage jumping after a cell swap on the NWZ-ZX1

The NWZ-ZX1 uses a voltage-threshold gauge — it estimates charge level by reading cell voltage at fixed points, not by counting coulombs. When a new cell goes in, the player's stored reference table no longer matches the new cell's discharge curve. That mismatch causes the indicator to jump or stall in the first few cycles. Run two or three full charge-to-discharge cycles and the gauge recalibrates. After that, the readout tracks accurately from 4.2V down to the cutoff threshold.

Playback cutting out before the battery indicator shows empty

The NWZ-ZX1's audio amplifier draws a short current spike on loud passages, especially at high gain with headphones under 32Ω impedance. At the tail end of discharge, cell voltage sags under that spike and dips below the BMS cutoff threshold momentarily, which shuts playback down even though the indicator still shows a few percent remaining. This is a cell voltage issue, not a firmware bug. A fresh US453759 cell holds its voltage flatter through the discharge curve, pushing that sag point lower. If cutouts persist on a new cell, check that the player is running firmware version 1.20 or later, which adjusts the cutoff trigger timing.