Acer Aspire M3 Replacement Battery AP12A3i 11.1V 4850mAh

Acer Aspire M3 / M5 Timeline Ultra — 11.1V Li-Polymer Replacement Battery (AP12A3i)

This is an 11.1V, 4850mAh (53.84Wh) Li-Polymer replacement battery for the Acer Aspire M3 and Aspire M5 Timeline Ultra notebook series. It matches OEM part numbers AP12A3i, AP12A4i, KT.00303.002, BT.00304.011, and 3ICP7/67/90. The cell is a direct fit for the ultrathin chassis and uses the same connector and BMS handshake as the original unit.

• M3 and M5 Timeline Ultra platform: Both the Aspire M3 and M5 Timeline Ultra share the same 11.1V three-cell configuration, connector pinout, and BMS communication protocol — which is why one part number covers both lines. Swapping between these models carries no compatibility risk at the hardware level.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on an Aspire M3 unit. The BMS negotiated charge current correctly, thermals stayed within spec across the pack, and the fuel gauge IC accepted the new cell without an error state after a calibration cycle.
• Post-install calibration on Acer Timeline Ultra: After fitting this battery, run the laptop down to hibernate-cutoff on battery alone — no AC — 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.

BIOS reporting poor battery health immediately after fitting a new cell

The Acer BIOS reads health data from EEPROM stored in the battery's BMS, not from live cell measurements. When a new cell arrives, that EEPROM data does not yet reflect real-world charge cycles on this specific unit. The firmware flags the mismatch as a fault before any calibration has run. One full discharge-to-hibernate followed by an uninterrupted charge to 100% rewrites the cycle data and clears the warning. After two to three of these cycles, the health percentage reported in Acer Care Center will stabilise.

Laptop shuts down at 20–30% remaining on the gauge

This happens when the fuel gauge IC's internal charge map still reflects the old cell's degraded voltage curve. Under combined CPU and display load, the new cell's actual voltage at 20–30% state-of-charge is higher than the threshold the firmware expects — but the gauge has not yet re-mapped those points. The laptop interprets the voltage-load relationship as a cliff and triggers a shutdown. Running two full calibration cycles — full discharge to hibernate, full uninterrupted charge — forces the fuel gauge IC to rebuild its lookup table against the new cell chemistry. After calibration, the shutdown threshold should return to 5% or below.