Sony NW-WM1A Replacement Battery 3.7V 1900mAh Li-Polymer

Sony NW-WM1A / NW-WM1Z — 3.7V Li-Polymer Replacement Battery (1-853-588-15)

This is a 3.7V, 1900mAh (7.03Wh) Li-Polymer replacement battery for the Sony NW-WM1A and NW-WM1Z Walkman digital audio players. It fits the internal battery bay directly and matches the OEM part numbers 1-853-588-15 and LIS1626HNPC. Swap this in when the original cell no longer holds a usable charge across a listening session.

• NW-WM1A and NW-WM1Z compatibility: Both the WM1A and WM1Z use the same 3.7V cell format, connector pinout, and BMS handshake. The WM1Z is the flagship copper-body variant; internally, the battery bay and charging circuit are identical, so the same replacement cell works in both.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a WM1A unit. The BMS accepted the cell without fault flags, and the charge circuit stepped through its expected CC/CV phases correctly. No protection-mode lockouts occurred at end-of-discharge.
• Post-swap charge sequence for the WM1A: After installing a fresh cell, connect the WM1A to its charger before powering on. If the old battery was deeply discharged, the device may sit in trickle-charge mode for up to 30 minutes before it accepts normal current. Do not force a boot during that window — the BMS needs to confirm minimum cell voltage before handing off control to the main board.

Battery percentage jumping after cell swap on the WM1A

The WM1A uses a voltage-threshold fuel gauge, not a coulomb counter. When a new cell goes in, the device has no charge history to work from, so it estimates state-of-charge from open-circuit voltage alone. This causes the displayed percentage to jump — sometimes from 40% to 90% within a few minutes of use. Run two or three full charge-to-discharge cycles and the gauge will stabilise. After the third cycle, readings should track within roughly 5–10% of actual capacity.

Playback cutting out before the battery indicator reaches empty

The WM1A's audio output stage draws a spike of current during high-gain, high-volume playback — particularly through balanced output. Near the bottom of the discharge curve, cell voltage sags under that load and can drop below the BMS cutoff threshold momentarily, triggering a shutdown even though the indicator still shows residual charge. This is a voltage-sag issue, not a capacity issue. If playback cuts at high volume but resumes after a short rest, reduce output gain or switch from balanced to single-ended output to lower the current draw. If it persists, check that the replacement cell voltage reads at least 3.5V under no-load before charging.