About this replacement
Toshiba Dynabook BJ65/FS — 11.4V Li-Polymer Replacement Battery (PA5344U-1BRS)
This is an 11.4V, 3750mAh (42.75Wh) Li-Polymer battery for the Toshiba Dynabook BJ65/FS notebook. It replaces OEM part PA5344U-1BRS and restores portable operation when the original cell has degraded or failed. Dimensions are 190.50 × 102.80 × 7.00mm — verify clearance before ordering if the bay has been modified.
- Dynabook BJ65/FS compatibility: The BJ65/FS uses a three-cell Li-Polymer pack on an 11.4V rail with a proprietary SMBus connector. This battery matches that rail voltage, physical footprint, and connector pinout so the BMS handshake completes on first boot.
- Bench tested on actual hardware: We ran this cell through charge, full-load discharge, and BMS communication checks. The BMS flagged no fault codes, cell balancing held within spec across all three cells, and the pack reported correct Wh data to the host system.
- Post-install calibration on the BJ65/FS: After fitting, run one full discharge to hibernate-cutoff — do not interrupt it — then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning the firmware shows after any cell swap on this model.
Why the BJ65/FS BIOS reports poor battery health immediately after a cell swap
The BJ65/FS stores learned battery data — cycle count, capacity history, and health flags — in EEPROM on the old pack. When a new cell goes in, the BIOS reads that register as empty or mismatched and flags the battery as degraded. This is not a fault with the replacement cell. Running the full discharge-to-hibernate then uninterrupted charge sequence gives the BIOS enough data to rewrite the health register. After one or two complete cycles, the health indicator returns to normal.
BJ65/FS shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC is still calibrated to the old cell's voltage curve. The gauge reads 25% but the actual cell voltage has already dropped below the BMS cutoff threshold under combined CPU and display load. The laptop cuts power before the screen shows zero. Fix it by completing two full discharge-to-hibernate cycles without interruption — this forces the fuel gauge IC to map the new cell's actual voltage cliff. After the second cycle, the shutdown point and displayed percentage will align, typically at or below 5%.