About this replacement
Sony VAIO VGN-AX570G Series — 11.1V Li-ion Replacement Battery (VGP-BPS4)
This is an 11.1V, 4400mAh (48.84Wh) Li-ion battery built to the VGP-BPS4 / VGP-BPS4A specification. It fits Sony VAIO VGN-AX and VGN-BX series laptops, including the VGN-AX570G, VGN-AX580G, VGN-BX143C, and VGN-BX143CP, among others. It slots into the original bay and connects to the existing charge circuit without modification.
- VGN-AX and VGN-BX platform fit: Sony used the same 11.1V three-cell rail, identical connector pinout, and shared BMS handshake protocol across the AX and BX chassis lines. That common electrical spec is why a single OEM part number — VGP-BPS4 — covers both series.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a VGN-BX unit. The BMS negotiated correctly, charge current tapered at capacity without tripping an overcharge fault, and the protection circuit responded to a simulated short without latching off permanently.
- VAIO battery learn cycle after install: After fitting this cell, run one full discharge to hibernate cutoff, then charge uninterrupted to 100% before using the laptop on AC again. Sony's BIOS battery learn cycle reads EEPROM data from the new cell during this first full pass — skipping it often leaves the fuel gauge stuck at an incorrect percentage or triggers a false health warning.
BIOS reporting poor battery health immediately after fitting a new cell
Sony's BIOS reads stored health data from the battery's EEPROM at boot. A brand-new cell carries factory EEPROM values that don't match the charge history the BIOS expects, so it flags the battery as degraded before a single cycle has run. This is a data mismatch, not a fault with the cell. Run one full discharge-to-hibernate followed by an uninterrupted charge to 100% — the BIOS recalibrates against the new EEPROM baseline and clears the warning on next boot.
Laptop shuts down abruptly at 20–30% charge shown on screen
This happens when the cell voltage drops below the BMS cutoff threshold under combined CPU and display load, even though the OS fuel gauge still shows charge remaining. The fuel gauge IC is calculating from an outdated capacity model tied to the old cell. The displayed percentage and the actual cell voltage are no longer tracking together. Complete two full calibration cycles — discharge to hibernate cutoff, charge to 100% each time — and the fuel gauge IC will re-anchor its model to the new cell's actual voltage curve.