About this replacement
Toshiba Qosmio X770 Series — 14.4V Li-ion Replacement Battery (PA3928U-1BRS)
This is a 14.4V, 4400mAh Li-ion replacement battery for the Toshiba Qosmio X770 gaming and multimedia notebook. It replaces OEM part numbers PA3928U-1BRS, PABAS248, and 4IMR19/65-2. Total energy capacity is 63.36Wh.
- Qosmio X770 series fit: The X770, X770-107, X770-11C, X770-136, and 17 additional X770 variants all share the same battery bay dimensions, 14.4V voltage rail, and SMBUS connector pinout. One cell fits the entire run of that chassis.
- Bench tested on actual hardware: We ran this cell through charge-discharge cycles on an X770 unit. The BMS communicated correctly over SMBUS, the BIOS accepted the cell without unknown-device errors, and charge termination triggered cleanly at full capacity.
- First-cycle learn reset on the X770: After fitting this cell, run the laptop on battery until it hibernates at low charge cutoff, then charge uninterrupted to 100%. The X770 BIOS runs a battery learn cycle against this data — skipping it leaves the fuel gauge IC working from the old cell's EEPROM figures, which causes wildly inaccurate state-of-charge readings for the first several uses.
Why the X770 BIOS flags a new battery as poor health
The Qosmio X770 stores battery health data in EEPROM on the original cell's protection circuit. When a new cell goes in, the BIOS reads no matching cycle count or rated-capacity record and flags the battery as degraded or unknown. This is a data mismatch — not a fault with the replacement cell. Running one full discharge-to-hibernate followed by an uninterrupted charge cycle writes new reference data to the BIOS learn table and clears the warning on most X770 firmware versions.
X770 shutting down at 20–30% charge shown on screen
The X770 pairs a high-draw CPU and discrete GPU that spike combined load far above idle draw. At 20–30% state-of-charge, a degraded or uncalibrated cell hits a voltage cliff — pack voltage drops below the BMS cutoff threshold under that load even though the fuel gauge still shows capacity remaining. The system interprets the voltage drop as an emergency and cuts power instantly. After installing a new cell, complete the learn cycle described above so the fuel gauge IC recalibrates its discharge curve against the fresh chemistry. Once calibrated, the gauge and the BMS threshold align, and the false shutdown clears.