JNC SSF-F5100 Compatible Battery 3.7V 450mAh Li-ion

JNC Sony Walkman SSF-F5100 — 3.7V Li-ion Replacement Battery

This is a 3.7V Li-ion replacement battery for the Sony Walkman SSF-F5100 portable media player. Capacity is 450mAh (1.67Wh), matching the original cell specification. It fits directly into the SSF-F5100 and restores full device functionality when the original cell has degraded.

• SSF-F5100 platform fit: The SSF-F5100 uses a single-cell 3.7V Li-ion pack with a simple two-wire or three-wire connector. No BMS handshake or proprietary authentication is required — the device reads voltage directly to determine charge state.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a media player test rig. The BMS protection circuit triggered correctly at the low-voltage cutoff threshold, and the cell accepted a full charge without thermal anomaly.
• First-use charge procedure for SSF-F5100: After installing this cell, connect the charger before attempting to power on. If the player has been sitting discharged for weeks, it may enter deep discharge protection and require 20–30 minutes of trickle current before the device responds to the power button.

Battery percentage jumping after cell swap on the SSF-F5100

After replacing the cell, the SSF-F5100's charge indicator may read 80% one moment and drop to 20% the next. This happens because the player's fuel gauge is calibrated to the discharge curve of the old, degraded cell. The new cell has a flatter voltage curve across its actual capacity range, which the indicator misreads as erratic state-of-charge. Run two or three full charge-to-discharge cycles and the indicator will recalibrate to the new cell's curve.

Playback cutting out before the battery indicator shows empty

At the tail end of discharge, cell voltage drops below the threshold the audio amplifier needs to drive the output stage cleanly. The player cuts audio or shuts down even though the indicator still shows a partial charge. This is a voltage-sag issue, not a capacity issue — the cell still holds charge, but instantaneous voltage under amplifier load dips below the cutoff. If this happens early in the cell's life, check that the connector is fully seated; a loose contact adds resistance and accelerates voltage sag under load.