About this replacement
Acer Aspire S5-391 Series — 14.8V Li-Polymer Replacement Battery (AP12B3F)
This is a 14.8V, 2300mAh (34.04Wh) lithium-polymer replacement battery for the Acer Aspire S5 and Aspire S5-391 ultrabook series. It fits the Aspire S5-391-6836, Aspire S5-391-73514G25akk, and related S5-391 variants. OEM cross-references include AP12B3F, BT.00403.022, and AP11B3F.
- Aspire S5-391 platform fit: All S5-391 variants share the same 14.8V battery rail, connector pinout, and BMS handshake protocol. One cell fits the full S5-391 range without modification or adapter.
- Bench tested on actual hardware: We ran this cell through charge-discharge cycles on the S5-391 platform. The BMS completed a full handshake, charge acceptance was confirmed across the full voltage range, and no protection cutoff events occurred during load testing.
- Post-install calibration on the S5-391: After fitting this battery, run a 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 this platform.
Why the Aspire S5-391 reports poor battery health immediately after a cell swap
The S5-391 BIOS reads battery health data stored in the old cell's EEPROM and caches it. When a new cell is installed, that cached data does not match the new cell's charge profile, triggering a false "poor health" or "unknown battery" flag. This is not a fault with the replacement cell — it is a calibration state. Running one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100% forces the BIOS to rewrite its battery learn data against the new cell. After one or two cycles, the health indicator normalises.
Aspire S5-391 shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC's charge map is still calibrated to the old, degraded cell. The IC predicts remaining capacity using a curve built from cycles on the previous battery, so the percentage shown does not reflect actual cell voltage. Under combined CPU and display load, the cell hits its real voltage floor before the gauge reaches 0%, and the system cuts power to protect itself. Run two full discharge-to-hibernate-cutoff cycles, charging fully between each, to force the fuel gauge IC to rebuild its map against the new 14.8V cell. After recalibration, shutdown should not occur above approximately 3.0V per cell.