About this replacement
MSI Alpha 15 Series — 15.4V Li-Polymer Replacement Battery (BTY-M55)
This is a 15.4V, 5800mAh (89.32Wh) Li-Polymer replacement battery for the MSI Alpha 15 A3DDK, A4DEK, B5EEK, and B5Ex gaming laptops. It replaces OEM part numbers BTY-M55 and 925QA055H. Fit this when the original cell no longer holds a usable charge or shuts the system down unexpectedly under load.
- Alpha 15 A3DDK through B5Ex compatibility: These four models share the same battery bay dimensions, connector pinout, and BMS communication protocol. The 15.4V four-cell configuration matches the voltage rail MSI uses across this Alpha 15 generation, so the replacement slides in without a firmware conflict.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Alpha 15 platform. The BMS handshake completed correctly on first boot, the charging IC accepted the new cell without fault codes, and capacity reporting initialised through the SMBus without intervention.
- BIOS learn cycle after install: After fitting this cell, run one full discharge until the laptop hibernates, then charge uninterrupted to 100% before use. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears after every cell swap on MSI's Alpha series.
Laptop shuts down at 20–30% shown after battery swap
This is a voltage cliff issue, not a faulty cell. Under combined CPU and GPU load — common during gaming on the Alpha 15 — current draw spikes sharply. If the fuel gauge IC has not yet calibrated against the new cell's discharge curve, it reads the remaining charge too high. The cell voltage drops below the BMS cutoff threshold before the displayed percentage reaches zero, triggering an abrupt shutdown. Run two full discharge-to-hibernate and uninterrupted charge cycles to give the fuel gauge IC enough data to map the new cell accurately.
BIOS reporting battery Wh rating as wrong after replacement
The Wh figure shown in BIOS or system info comes from EEPROM data embedded in the battery's BMS chip, not from a live cell measurement. On a new replacement cell, the EEPROM may report the rated chemistry value rather than the exact figure listed on the label. This is a data-field mismatch, not a capacity defect — actual deliverable energy is unchanged. If the displayed Wh is within 5% of the rated 89.32Wh after two calibration cycles, the cell is performing correctly.