About this replacement
Acer Aspire One 531 / 751 Series — 11.1V Li-ion Replacement Battery (UM09A41)
This 11.1V, 4400mAh (48.84Wh) Li-ion battery replaces the original cell in the Acer Aspire One 531 and Aspire One 751 netbook series. It covers OEM part numbers UM09A41, UM09B7C, UM09B31, UM09B34, UM09B7D, UM09A31, UM09A71, UM09A73, UM09A75, UM09B71, and UM09B73. If your netbook no longer holds charge or shuts off unexpectedly, this is the direct cell replacement.
- Aspire One 531 and 751 platform fit: Both the 531 and 751 share the same 11.1V three-cell battery bay, connector pinout, and BMS handshake protocol — which is why a single part number covers the full range. Swapping between these models is not an issue at the hardware level.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on an Aspire One 751. The BMS negotiated correctly, the BIOS accepted the cell without a fault flag, and the fuel gauge tracked state-of-charge without erratic jumps after the first calibration cycle.
- First-cycle calibration on the Aspire One: After fitting, run one full discharge to hibernate cutoff, then charge uninterrupted to 100%. This forces the Aspire One's fuel gauge IC to re-learn the new cell's capacity curve and clears the false "poor battery health" warning that appears in Acer's power management after any cell swap.
BIOS reporting poor battery health immediately after fitting a new cell
The Aspire One stores battery health data in EEPROM on the old cell. When a new cell is fitted, the BIOS reads that data as missing or mismatched and flags the battery as degraded — even though the cell is new. This is a firmware artefact, not a hardware fault. Running one complete discharge-to-hibernate then a full uninterrupted charge resets the learn cycle. After two to three cycles, the BIOS health indicator will update to reflect the actual cell condition.
Netbook shuts down at 20–30% charge shown on the fuel gauge
This happens when the fuel gauge IC has not yet calibrated against the new cell's voltage curve. The gauge shows 25% remaining, but the cell voltage has already dropped below the BMS cutoff threshold under CPU and display load — so the system shuts off without warning. It is not a faulty cell. Run two full discharge-to-hibernate cycles followed by complete charges, letting the gauge IC map the new cell's actual voltage floor. After calibration, the gauge and BMS cutoff will align — target a resting voltage of 11.1V at full charge to confirm the cell is performing correctly.