Acer Extensa 392C Replacement Battery BTP-231 10.8V 4000mAh

Acer Extensa 392C Series — 10.8V Ni-MH Replacement Battery (BTP-231)

This is a 10.8V, 4000mAh Ni-MH replacement battery for the Acer Extensa 392C notebook. It also fits the Extensa 391C, AcerNote 393, AcerNote 390A, and more than 20 additional models sharing the same battery bay and connector. OEM part numbers covered include BTP-231, BTP-031, 60.43A01.021, 91.40B28.001, and 91.43A28.004.

• Extensa and AcerNote compatibility: These models share a common 10.8V three-cell Ni-MH battery platform with an identical physical connector and charge-management circuit. The BMS handshake is handled by the motherboard, not the cell pack, so any cell meeting the voltage and form factor spec works across the full lineup.
• Bench tested on actual hardware: We ran this cell on an Extensa 392C and monitored charge acceptance across three full cycles. The BMS accepted charge without fault flags and the pack reached rated capacity by the third cycle without thermal event.
• First-cycle conditioning for Ni-MH cells: After installing, run one full discharge down to the BIOS hibernate cutoff, then charge uninterrupted to 100%. Ni-MH cells need this conditioning cycle — skipping it leaves the fuel gauge IC reading against the old cell's data and the BIOS will flag a health warning that won't clear on its own.

BIOS reporting poor battery health after swapping the Extensa cell pack

The Extensa BIOS stores learned capacity data from the previous cell pack in EEPROM. When a new cell goes in, the BIOS compares live readings against that stored baseline and immediately flags poor health — even on a brand-new pack. This is not a fault with the replacement cell. Running a full discharge-to-cutoff followed by an uninterrupted charge to 100% forces the BIOS battery learn cycle to overwrite the old EEPROM data with values from the new cell. After one or two complete cycles, the health warning clears and reported capacity stabilises at the correct figure.

Laptop shuts down at 20–30% charge shown on screen

This symptom almost always points to a calibration gap between the fuel gauge IC and the new cell, not a defective pack. The fuel gauge IC tracks charge state against a capacity model built from the old cell's discharge curve — when the new cell's actual voltage cliff doesn't match, the laptop cuts out before the gauge reaches zero. Run two full discharge-to-hibernate cycles without interrupting the charge phase. By the second cycle, the fuel gauge IC recalibrates its discharge curve against the new cell and the premature shutdowns stop. If the laptop still cuts out after two calibration cycles, check that the AC adapter output holds steady at 19V under load.