About this replacement
Asus U305CA6Y30 Series — 11.4V Li-Polymer Replacement Battery (C31N1411)
This is an 11.4V, 3800mAh (43.32Wh) lithium-polymer replacement battery for the Asus U305CA6Y30 and related U305 series ultrabooks. It replaces OEM part numbers C31N1411 and 0B200-01180000. The battery sits in the internal bay and powers the laptop during portable use.
- U305 series compatibility: The U305CA6Y30, U305F, U305FA5Y10, and U305FA5Y71 all use the same 11.4V three-cell polymer architecture and share the same BMS handshake protocol. Any unit in this range accepts the same physical pack and connector pinout.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a U305 unit. The BMS accepted the pack without flags, the fuel gauge IC began tracking normally, and cell voltage held steady across the discharge curve without early cutoff.
- First-cycle calibration after install: After fitting this battery, run the laptop down to hibernate cutoff under normal use — do not force shutdown — then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health or capacity warning that appears after every cell swap.
BIOS reporting battery health as poor immediately after replacement
The BIOS reads health data from EEPROM registers written by the original cell. When a new cell goes in, those registers hold stale degradation data from the old pack. The BIOS flags the battery as poor or unknown because it is comparing real-time readings against a worn-cell baseline. Running one full discharge-to-hibernate then a complete uninterrupted charge lets the firmware rewrite those registers against the new cell's actual profile. After one or two cycles, the health indicator returns to normal.
Laptop shuts down abruptly at 20–30% charge shown
This happens when the fuel gauge IC has not yet calibrated against the new cell's chemistry. The reported percentage drifts ahead of the actual cell voltage, so the pack hits its low-voltage cutoff while the OS still shows 20–30% remaining. The fix is calibration: discharge fully to automatic hibernate, then charge to 100% without interruption — repeat this two to three times. After calibration cycles, the gauge aligns with real cell voltage and the shutdowns stop.