Asus Eee PC S101H Replacement Battery AP21-1002HA 7.4V

Asus Eee PC S101H Series — 7.4V Li-Polymer Replacement Battery (AP21-1002HA)

This is a 7.4V, 4200mAh (31.08Wh) Li-Polymer battery for the Asus Eee PC S101H and 1002HA netbook line. It replaces OEM part AP21-1002HA directly. The flat Li-Polymer cell pack fits the shallow battery bay these compact netbooks use.

• Eee PC 1002 and S101H fitment: These models share the same 7.4V two-cell Li-Polymer configuration, identical connector pinout, and the same BMS communication protocol over the SMBus line. A battery built for one works in all variants listed.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on an Eee PC 1002HA. The BMS handshake completed without error, charge acceptance reached full capacity, and the SMBus data reported correct voltage and state of charge to the OS fuel gauge.
• First-cycle discharge routine on the Eee PC: After installing, let the netbook run on battery until it hibernates at cutoff, then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell data and clears the inaccurate health warning that appears after every cell swap.

BIOS reporting poor battery health after fitting the AP21-1002HA

The Eee PC reads health data stored in the battery's EEPROM and compares it against learned cycle data from the previous cell. A new cell has a clean EEPROM, so the BIOS flags a mismatch as poor health immediately after swap. This is not a fault with the replacement cell. Running one complete discharge-to-hibernate followed by a full uninterrupted charge resets the learn cycle and clears the warning. After two to three full cycles the BIOS health indicator stabilises.

Eee PC shutting down at 20–30% charge remaining

This happens when the fuel gauge IC has not yet calibrated its capacity estimate against the new cell's actual chemistry. The old cell's discharge curve data is still cached, so the percentage reading drifts early and the netbook hits the low-voltage shutdown threshold before the display reaches zero. Run two full discharge-to-hibernate cycles with the screen at normal brightness to force the IC to map the new voltage cliff. After calibration the shutdowns stop and the gauge reads correctly down to the cutoff voltage near 6.0V.