About this replacement
Sony VAIO VGN-U50 / VGN-U70 Series — 11.1V Li-Polymer Replacement Battery (VGP-BPS1)
This is an 11.1V 2100mAh lithium-polymer replacement battery for the Sony VAIO U-series ultraportable notebooks. It fits the VGN-U50, VGN-U70, VGN-U8G, and VGN-U8C, among other U-series variants. OEM part numbers VGP-BPS1 and VGP-BPL1 both cross-reference this cell.
- U-series platform compatibility: These models share an identical battery bay geometry, connector pinout, and BMS communication protocol — the same 11.1V Li-Polymer cell services the entire U-series line without modification.
- Bench tested on actual hardware: We ran this cell on a VGN-U50 and monitored BMS handshake via the SMBus line. Charge acceptance was clean from 0V recovery through to termination, and the protection circuit tripped correctly at both over-voltage and over-temperature thresholds.
- Post-installation discharge cycle: After fitting this battery, 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 U-series hardware.
VAIO VGN-U50 shutting down at 20–30% charge shown
This happens when the fuel gauge IC still holds calibration data from the degraded original cell. The new cell hits a voltage cliff under combined CPU and display load before the gauge catches up. The system interprets the sudden voltage drop as empty and forces shutdown. Run two full discharge-to-hibernate then charge-to-100% cycles — the fuel gauge IC recalibrates against the new cell's actual voltage curve and the shutdowns stop.
BIOS reporting battery health as poor or unknown after swap
The VAIO BIOS reads cycle count, rated Wh, and health status from EEPROM data embedded in the battery's BMS. On first installation, the BIOS compares stored EEPROM values against its last logged readings from the old cell — mismatch triggers a "poor" or "unknown" health flag. This is a data comparison artefact, not a fault with the new cell. Complete the full discharge-recharge learn cycle and the BIOS health readout will update to reflect the actual state of the replacement cell.