About this replacement
Samsung ATIV Book 9 Spin 900X5L Series — 7.7V Li-Polymer Replacement Battery (AA-PBUN4AR)
This 7.7V, 5100mAh (39.27Wh) lithium-polymer cell replaces the OEM battery in the Samsung ATIV Book 9 Spin and 900X5L series convertible laptops. It fits models including the 900X5L-K01 and 900X5L-K02, along with 249 additional variants sharing the same AA-PBUN4AR specification. The slim 5.10mm profile matches the original pack geometry for the 2-in-1 chassis.
- 900X5L platform compatibility: The 900X5L series uses a shared 7.7V power rail and a proprietary connector that keys to the AA-PBUN4AR pack. Every model in this lineup communicates with the BIOS through the same BMS handshake protocol, so one cell covers the entire family without modification.
- Bench tested on actual hardware: We ran this cell on a 900X5L unit and monitored BMS communication through full charge and discharge cycles. The protection circuit responded correctly to cell voltage boundaries at both ends, and the BIOS accepted the battery without throwing an unknown-device flag.
- Post-install discharge cycle on the ATIV Book 9 Spin: After fitting this battery, run one full discharge down to the automatic hibernate cutoff, then charge uninterrupted to 100% before using the device normally. The BIOS battery learn cycle resets against the new cell's actual capacity — skipping this step causes the fuel gauge to read incorrectly for the first week of use.
BIOS reporting poor battery health immediately after installation
The ATIV Book 9 Spin's BIOS stores charge history and health data in the old cell's EEPROM. When a new cell goes in, the BIOS compares the blank EEPROM against the accumulated wear data it expects and flags the result as degraded. This is a data mismatch, not a cell fault. Running the battery learn cycle — one full discharge to hibernate cutoff followed by an uninterrupted charge to 100% — gives the BIOS enough real data to recalculate health from zero. After two to three full cycles, the health indicator stabilises at its correct value.
Laptop shuts down at 20–30% charge shown on the gauge
This happens when the fuel gauge IC hasn't yet mapped the new cell's actual voltage curve. The gauge reports 25% remaining while the cell voltage has already dropped below the load threshold the system needs to sustain the CPU and display together. The BMS trips the cutoff before the OS can gracefully shut down. Run two to three calibration cycles — full discharge to hibernate cutoff, then full charge to 100% each time — until the shutdown point drops to single-digit percentages or the cell reaches the 3.0V per cell floor at the correct gauge reading.