About this replacement
Panasonic Toughbook CF-MX4 / CF-MX3 / CF-MX5 — 7.2V Li-ion Replacement Battery (CF-VZSU92)
This is a 7.2V, 4400mAh (31.68Wh) Li-ion battery for the Panasonic Toughbook CF-MX4, CF-MX3, and CF-MX5 convertible laptops. It replaces OEM part numbers CF-VZSU92, CF-VZSU92E, CF-VZSU92JS, CF-VZSU92R, CF-VZSU93JS, and VZSU92JS. The connector, BMS handshake protocol, and voltage rail match the original Panasonic specification.
- CF-MX3, CF-MX4, and CF-MX5 compatibility: These three Toughbook convertible generations share the same 7.2V battery bay, connector pinout, and BMS communication protocol — which is why one cell covers all three platforms. The BMS on each model reads the same EEPROM identifiers and accepts the handshake without error.
- Bench tested on actual hardware: We ran this cell on a CF-MX4 unit through charge-discharge cycles and confirmed the BMS completed a full charge without tripping the protection circuit. The fuel gauge IC communicated correctly and the BIOS battery status panel registered a valid cell at rated voltage.
- First-cycle calibration on the CF-MX4: After fitting this cell, run the Toughbook down to hibernate cutoff under normal use — display on, Wi-Fi active — then charge uninterrupted to 100%. This forces the CF-MX4's BIOS battery learn cycle to reset against the new cell's actual capacity and clears the inaccurate health warning that appears after every cell swap.
BIOS reporting poor battery health immediately after fitting a new cell
The CF-MX4 BIOS reads health data stored in the outgoing cell's EEPROM and compares it against the new cell on first boot. Because the new cell carries different cycle-count and capacity data, the BIOS flags it as degraded before any calibration has run. This is not a fault with the replacement cell — it is a data mismatch between old EEPROM history and a fresh chemistry. Run one full discharge-to-hibernate cycle followed by an uninterrupted charge to 100% and the BIOS health indicator will update correctly.
Toughbook shutting down at 20–30% charge shown on screen
When the CF-MX4 runs under combined CPU and display load — field data entry, map rendering, video conferencing — power draw spikes sharply. If the fuel gauge IC has not yet calibrated against the new cell, it maps those draw spikes to the old cell's voltage curve and triggers an early shutdown before the cell is actually depleted. The fix is calibration: discharge fully to hibernate, charge uninterrupted to 100%, and repeat once more if the gauge remains off. After two complete cycles the fuel gauge IC locks onto the correct voltage-to-capacity curve and the early cutoff stops.