About this replacement
Panasonic CF-RZ4 / CF-RZ8 Series — 7.6V Li-Polymer Replacement Battery (CF-VZSU0EJS)
This 7.6V, 4850mAh (36.86Wh) lithium-polymer battery replaces the CF-VZSU0EJS cell in the Panasonic Toughbook CF-RZ4, CF-RZ5, CF-RZ6, and CF-RZ8. These are compact rugged ultraportables used in field and enterprise environments where a degraded cell kills portability fast. Voltage and capacity match OEM spec exactly — no firmware workarounds needed.
- CF-RZ4 through CF-RZ8 compatibility: All four models share the same 7.6V Li-Polymer cell format, connector pinout, and BMS handshake protocol — Panasonic carried the same battery platform across this rugged ultraportable line without changing the charge circuit.
- Bench tested on actual hardware: We cycled this cell through the CF-RZ4 charge controller and confirmed the BMS negotiated correctly, accepted a full charge, and released discharge current without triggering a protection cutoff.
- Post-install calibration cycle on the CF-RZ4: 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 the CF-RZ series throws after every cell swap.
Why the CF-RZ4 BIOS reports poor battery health after a cell swap
The CF-RZ series stores charge history and health metrics in EEPROM on the battery pack itself. When you fit a new cell, the BIOS reads that blank EEPROM and flags the battery as unknown or degraded — not because the cell is faulty, but because no history exists yet. Running the calibration cycle writes initial data to the fuel gauge IC and gives the BIOS something real to read. After two to three full cycles, the health flag clears and the reported capacity stabilises.
CF-RZ4 shutting down at 20–30% charge shown on screen
This happens when the fuel gauge IC has not yet calibrated against the new cell's actual voltage curve. The OS reads the old curve, thinks 25% is safe, but the cell voltage drops below the BMS cutoff threshold under combined CPU and display load — and the system cuts out. It is not a faulty cell. Run one full discharge to hibernate-cutoff without interruption, then charge to 100%. That single cycle gives the fuel gauge IC enough data to remap the curve accurately to the new cell.