IBM ThinkPad 365 Replacement Battery 9.6V 4000mAh 38H6304

IBM ThinkPad 365 Series — 9.6V Ni-MH Replacement Battery (38H6304)

This is a 9.6V, 4000mAh Ni-MH replacement battery pack for the IBM ThinkPad 365 series notebooks. It fits the ThinkPad 365, 365C, 365CD, and 365CS, among other models in the 365 line. OEM part numbers covered include 38H6304, 41H8136, 41H8165, and FRU 41H7438.

• ThinkPad 365 series compatibility: All models in the 365 line share the same battery bay geometry, connector pinout, and 9.6V rail requirement. The BMS handshake is identical across the 365, 365C, 365CD, and 365CS, so one cell pack covers the full series without modification.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a ThinkPad 365-class machine. The BMS accepted charge from cold, held voltage under display-plus-CPU load, and tripped the low-voltage cutoff cleanly without hard shutdown at the wrong threshold.
• First-cycle calibration on ThinkPad 365: After installing, run the laptop on battery until it hibernates at the low-voltage cutoff, then charge uninterrupted to 100%. This single full cycle resets the BIOS battery learn cycle and clears the inaccurate capacity warning that appears after every pack swap on this platform.

Why the ThinkPad 365 BIOS reports poor battery health after a fresh cell swap

The ThinkPad 365 BIOS stores learned capacity data from the old pack in its battery EEPROM. When a new cell is installed, that stored data no longer matches actual cell chemistry, so the BIOS flags health as poor or unknown — even on a fully charged, functional pack. Running one complete discharge-to-hibernate followed by an uninterrupted full charge forces the firmware to rewrite the EEPROM with accurate data from the new Ni-MH cells. After two to three cycles, the reported health figure stabilises and the warning clears.

ThinkPad 365 shutting down at 20–30% charge shown on the fuel gauge

This happens when the Ni-MH cells hit a voltage cliff under combined CPU and display load before the fuel gauge IC registers empty. The fuel gauge was calibrated to the old, degraded pack and is reading the remaining charge against stale baseline data. The cell voltage drops below the BMS cutoff threshold — typically around 8.0V under load — before the gauge counts down to zero, triggering a hard shutdown. Run two full discharge-to-hibernate and full-charge cycles to recalibrate the fuel gauge IC against the actual voltage curve of the new cells.