Panasonic ToughBook CF-71 PII CMOS Replacement Battery 3V 200mAh

Panasonic ToughBook CF-71 PII / PIII — 3V Lithium CMOS Backup Battery

This is a 3V 200mAh lithium coin cell replacement for the CMOS backup circuit on the Panasonic ToughBook CF-71 PII and CF-71 PIII. It sits on the motherboard and powers the RTC and SRAM that hold your BIOS settings, system clock, and hardware configuration when the laptop is switched off. When the original cell depletes, the CF-71 loses all stored settings on every power cycle.

• CF-71 PII and PIII compatibility: Both the PII and PIII variants of the CF-71 share the same motherboard CMOS circuit, RTC architecture, and coin cell socket. The 3V retention voltage and physical footprint are identical across both generations, so one cell covers both.
• Bench tested on actual hardware: We ran this cell on the CF-71 motherboard and confirmed the BMS circuit accepted the new cell without triggering a checksum fault. The RTC held time across multiple cold boots once BIOS was saved after installation.
• Post-install BIOS reset required: After swapping the cell, enter BIOS immediately and set the correct date and time, then save and exit. The RTC circuit resets to a default value the moment the old cell is removed — the new cell will hold whatever time you set, but it cannot recover the previous clock value from a depleted cell.

BIOS clock resetting to 2000 after every power cycle on the CF-71

The CF-71 RTC circuit requires a minimum retention voltage of 2.8V from the CMOS cell to hold the clock and SRAM contents between power cycles. A depleted original cell typically measures between 2.2V and 2.6V — enough to pass a basic multimeter check but not enough to sustain the RTC overnight. The result is the clock rolling back to a default date, usually January 1, 2000, every time mains power is removed. Replacing the coin cell and resetting the clock in BIOS resolves this completely.

CMOS checksum error on boot after fitting a new coin cell

A checksum error immediately after installing a new cell usually means the CMOS SRAM has already been cleared — either the old cell was fully dead for an extended period, or the new cell was seated with the laptop fully unplugged and the residual charge on the board dissipated. The BIOS cannot reconstruct its configuration from an empty SRAM, so it flags the mismatch on boot. Clear the error by entering BIOS setup, reconfiguring any custom settings, and saving — the new cell will then hold the checksum correctly from that point forward.