About this replacement
Acer Aspire One 531 / 751 Series — 11.1V Li-ion Replacement Battery (UM09A41)
This 11.1V, 6600mAh Li-ion battery replaces the original cell in the Acer Aspire One 531 and Aspire One 751 netbooks. It cross-references OEM part numbers UM09A41, UM09B7C, UM09B31, UM09B34, UM09B7D, UM09A31, UM09A71, UM09A73, UM09A75, UM09B71, and UM09B73. Physical dimensions are 203.09 × 50.73 × 47.00mm — verify your bay clearance before fitting.
- Aspire One 531 and 751 platform fit: Both the 531 and 751 share the same 11.1V three-cell voltage rail, identical connector pinout, and the same BMS handshake protocol — that is why a single part number covers the full range. The 73.26Wh rating matches what the Aspire One charging circuit expects.
- Bench tested on actual hardware: We cycled this cell on an Aspire One 751 chassis. The BMS completed a full charge-to-cutoff sequence without tripping overcurrent protection, and the fuel gauge IC registered capacity correctly after two calibration passes.
- First-cycle calibration on the Aspire One: After fitting, run one full discharge down to hibernate-cutoff, then charge uninterrupted to 100% without removing AC power mid-cycle. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears on the first boot after any cell swap.
BIOS reporting battery health as poor immediately after fitting a new cell
The Aspire One BIOS reads EEPROM data written by the original factory cell. When a replacement cell arrives, that EEPROM profile does not match the new chemistry data, so the BIOS flags it as degraded before a single charge cycle runs. This is a data mismatch, not a fault with the battery. Running one complete discharge-to-hibernate followed by a full uninterrupted charge allows the BIOS learn cycle to overwrite the stale EEPROM values. After that cycle, the health indicator should clear and report normally.
Aspire One shutting down abruptly at 20–30% charge shown
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The IC still uses the old cell's discharge profile, so it misjudges the voltage cliff — the point where cell voltage drops sharply under CPU and display load — and triggers a hard shutdown earlier than expected. The fix is two to three full calibration cycles: discharge fully to hibernate, charge to 100% without interruption, repeat. By the third cycle, the fuel gauge tracking should align with actual remaining capacity and shutdowns at false-low percentages will stop.