About this replacement
Sony VAIO VGN-U50 / VGN-U70 Series — 11.1V Li-ion Replacement Battery (VGP-BPS1)
This 11.1V, 4200mAh Li-ion battery replaces the VGP-BPS1 and VGP-BPL1 cells in the Sony VAIO U-series ultra-portable laptops. It fits the VGN-U50, VGN-U70, VGN-U8G, VGN-U8C, and related U-series models. Capacity is 46.62Wh — matched to the original Sony specification.
- VAIO U-series compatibility: The VGN-U50, VGN-U70, VGN-U8G, and VGN-U8C all share the same 11.1V three-cell battery bay, connector pinout, and BMS handshake protocol — which is why one cell fits the full U-series lineup without modification.
- Bench tested on actual hardware: We cycled this cell on a VGN-U series unit and confirmed the BMS negotiated correctly, charge termination triggered at full capacity, and discharge protection cut in at the expected low-voltage threshold without premature shutdown.
- First-cycle calibration on VAIO U-series: After installing, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on this platform.
Why the VAIO VGN-U50 shuts down at 20–30% after a battery swap
The VGN-U50 uses a fuel gauge IC that retains learned voltage-curve data from the previous cell. When a new cell is installed, the old curve causes the gauge to misread remaining capacity — the laptop thinks 20% is the floor and initiates shutdown even though charge remains. The fix is a full discharge-to-hibernate followed by an uninterrupted charge to 100%. After two or three full cycles, the fuel gauge IC recalibrates against the new cell's voltage profile and the cutoff point corrects itself.
BIOS reports battery health as "poor" or capacity as 0% immediately after install
This happens because the BIOS reads health data from EEPROM fields written by the original cell — the new cell's EEPROM starts without a charge history, so the BIOS flags it as degraded. It is not a fault with the replacement cell. Run one full discharge-to-hibernate, then charge uninterrupted to 100% to initialize the learn cycle. After the first complete cycle, the BIOS health readout on the VGN-U series typically updates to reflect accurate capacity above 90%.