Thunderobot MixBook Air L140BAT-2 Compatible Battery 7.7V 4650mAh

Thunderobot MixBook Air — 7.7V Li-Polymer Replacement Battery (L140BAT-2)

This is a 7.7V, 4650mAh (35.81Wh) Li-Polymer replacement battery for the Thunderobot MixBook Air laptop. It fits directly in place of the original L140BAT-2 cell. When the factory battery no longer holds a charge or has degraded beyond use, this cell restores portable power to the machine.

• MixBook Air platform fit: The MixBook Air uses a slim single-cell Li-Polymer pack at 7.7V to match its thin-chassis power rail. The L140BAT-2 part number identifies the exact connector pinout and BMS handshake protocol — other voltages or connector types will not negotiate correctly with this board.
• Bench tested on actual hardware: We cycled this cell through charge and load on the MixBook Air platform. The BMS accepted the new cell without rejection, completed charge termination correctly at full voltage, and the fuel gauge IC began calibration as expected across the first few cycles.
• Post-install calibration on the MixBook Air: After fitting this cell, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears immediately after every cell swap on this platform.

BIOS reporting poor battery health immediately after fitting the L140BAT-2

The MixBook Air BIOS reads EEPROM data from the outgoing cell and flags a health warning when the new cell's EEPROM counters don't match the learned profile. This is a firmware-side mismatch, not a fault with the replacement cell. The fuel gauge IC needs two to three full charge-discharge cycles before it recalibrates its capacity model against the new chemistry. After those cycles, the health indicator and percentage readings normalise.

MixBook Air shutting down at 20–30% charge shown on screen

This happens when the cell's voltage drops sharply under combined CPU and display load before the fuel gauge reaches zero — a voltage cliff the old or degraded cell couldn't sustain. The BIOS triggers a shutdown to protect the board the moment rail voltage sags below threshold, even if the OS still shows charge remaining. On a new cell this usually resolves after the calibration cycle described above. If shutdown still occurs after three full cycles, check the BIOS power settings and confirm the battery learn cycle ran to completion from hibernate at 0%.