About this replacement
Asus VivoBook 15 X705 Series — 11.52V Li-Polymer Replacement Battery (B31N1635)
This is an 11.52V, 3600mAh (41.47Wh) lithium-polymer battery for the Asus VivoBook 15 X705 series. It fits a wide range of X705 variants including the X705UV-3G, X705NC-1B, and X705UV-1B. OEM part numbers B31N1635 and B0B200-02560000 both reference this cell.
- X705 series battery platform: The X705 line shares a unified battery bay and connector across its UV, NC, and related sub-variants. All run the same 11.52V three-cell architecture with an identical BMS handshake, so one cell covers the full model spread without adapter or modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on X705UV hardware. The BMS initialised cleanly, the protection circuit responded correctly to load spikes, and the fuel gauge IC accepted the new cell without throwing error codes.
- First-cycle calibration on the X705: After fitting, run the battery down until the laptop hibernates, then charge uninterrupted to 100% without using the machine. The X705 BIOS uses that full cycle to reset the battery learn table — skipping it leaves the health indicator stuck on a reading from the old cell.
Why the X705 BIOS flags a new battery as poor health immediately after swap
The X705 BIOS stores battery health data in EEPROM tied to the original cell's charge history. When a new cell is fitted, that stored data no longer matches the new cell's actual state, so the BIOS reads the mismatch as degradation. This is not a fault with the replacement battery — it is a calibration state. Running one full discharge-to-hibernate then an uninterrupted charge to 100% triggers the BIOS battery learn cycle, which overwrites the stale EEPROM data. After one or two complete cycles, the health status clears.
X705 shutting down at 20–30% charge shown on the gauge
This is a voltage cliff issue, not a calibration issue. Under full CPU and display load, the cell voltage drops faster than the fuel gauge IC can track — the laptop hits the low-voltage cutoff before the displayed percentage reaches zero. It happens most often when the battery hasn't completed a learn cycle and the IC is still mapping capacity against the old cell's curve. Run a full discharge to hibernate-cutoff and charge back to 100% without interruption. If the shutdowns persist past two calibration cycles, check that the cell voltage at shutdown is above 9.5V total — below that points to a genuine cell fault.