QN-J6BPS Sony CMD-J6 Replacement Battery 3.7V 700mAh Li-ion

Sony CMD-J6 / CMD-J26 — 3.7V Li-ion Replacement Battery (QN-J6BPS)

This is a 3.7V, 700mAh Li-ion replacement battery for the Sony CMD-J6 and CMD-J26 mobile phones. It replaces OEM part number QN-J6BPS and restores full power to both handsets. Fit the battery when the original no longer holds adequate charge for calls and messaging.

• CMD-J6 and CMD-J26 compatibility: Both phones share the same battery bay dimensions, connector pinout, and 3.7V supply rail. The QN-J6BPS part number covers both models, so one cell fits either handset without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the CMD-J6 platform. The BMS accepted the charge IC handshake on the first cycle, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The CMD-J6 fuel gauge IC was calibrated against the original cell's discharge curve — one full cycle resets that reference to the new cell so the percentage readout stays accurate.

Why the CMD-J6 reports wrong battery percentage after a cell swap

The CMD-J6 uses a fuel gauge IC that tracks charge state by counting coulombs against a stored discharge curve from the original cell. A new cell has a slightly different internal resistance and voltage profile, so the IC's stored reference no longer matches reality. The display can read anywhere from 10–30% off until the gauge relearns. One full discharge-to-shutdown followed by a full uninterrupted charge gives the IC a clean reference cycle and corrects the readout.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the BMS cutoff threshold under the load of an active call or backlight — even though the fuel gauge still shows charge remaining. The gauge is reporting a percentage based on a stale discharge curve, not the actual cell voltage. The cell hits roughly 3.0V under load and the protection circuit cuts output before the percentage reaches zero. Running one complete calibration cycle as described above tightens the gauge's voltage tracking and stops the early cutoff from appearing.