About this replacement
Toshiba Dynabook R730/B Series — 10.8V Li-ion Replacement Battery (PA3831U-1BRS)
This is a 10.8V, 4400mAh (47.52Wh) Li-ion battery for the Toshiba Dynabook R730/B, R731, R732, R741/B, and related thin-and-light business notebooks. It replaces OEM part numbers including PA3831U-1BRS, PA3832U-1BRS, PABAS235, PABAS249, and PA5043U-1BRS, among others. Physical dimensions are 206.10 × 43.45 × 19.90mm — confirm your original battery matches before installing.
- R730/R731/R732/R741 battery platform: These Dynabook models share a common 10.8V three-cell Li-ion battery bay, connector pinout, and BMS communication protocol. Toshiba assigned multiple OEM part numbers across production runs — PA3831U through PA3931U and the PABAS series — but the electrical spec and physical form factor are the same across all of them.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Dynabook R730-series unit. The BMS handshake completed correctly, charge termination triggered at full capacity, and the thermal cutoff circuit responded normally under sustained CPU load.
- Post-install recalibration on Dynabook firmware: After installing, run one full discharge down to the hibernate cutoff, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell. Skip this step and the fuel gauge IC will keep reading from stale EEPROM data — the system will report poor health or an inaccurate charge percentage from day one.
Why the Dynabook R730 BIOS flags a new battery as poor health
Toshiba's firmware stores battery health data in EEPROM on the old cell. When you swap the battery, the BIOS reads stale cycle count and capacity data that no longer matches the new cell's chemistry profile. The result is a "poor battery condition" warning even on a brand-new cell. Running one full discharge-to-hibernate followed by an uninterrupted full charge lets the firmware write fresh calibration data to the new cell's EEPROM. After one or two cycles, the health indicator normalises.
Dynabook R730 shutting down at 20–30% charge shown
This happens when the cell can no longer sustain voltage under the combined load of CPU activity and the display backlight. As the battery discharges, voltage drops — and under full draw it crosses the BMS low-voltage cutoff threshold before the fuel gauge reaches 0%. The gauge was calibrated against the old cell's discharge curve, so the percentage shown is wrong. Run the full discharge-to-hibernate recalibration cycle. After two full cycles, the fuel gauge IC maps the new cell's actual voltage curve and the premature shutdowns stop.