About this replacement
Sony VAIO PCG-GRX3P Series — 2.4V Ni-MH CMOS Backup Battery (PCG-91111M)
This is a 2.4V, 20mAh Ni-MH CMOS backup battery for Sony VAIO PCG-GRX series laptops, including the PCG-GRX3P, PCG-GRX550, PCG-GRX500P, and PCG-GRX560K. It powers the RTC circuit and SRAM that hold BIOS settings, system clock, and date when the laptop is off or unplugged. OEM part numbers covered include PCG-91111M, 2/V15H, Varta 2/V30H, 2/V20H, and FL2/V11H-WR.
- GRX series CMOS socket fit: These PCG-GRX models share a common motherboard CMOS circuit using a 2.4V Ni-MH cell at this exact form factor — 31.07 x 12.04 x 4.40 mm. Voltage and physical dimensions must match; substituting a 3V CR2032 here will overvolt the retention circuit.
- Bench tested on actual hardware: We confirmed the cell holds above the 2.8V RTC retention threshold under no-load standby and verified the connector mates correctly with the GRX series motherboard header without modification.
- Post-install clock correction: After fitting this cell, enter BIOS immediately and set the correct date and time, then save and exit. The RTC circuit powers down during the swap, resetting the clock to a factory default. Skipping this step means the system boots with a wrong date until you correct it manually.
BIOS clock resetting to a default date after every power cycle
When the CMOS cell drops below 2.8V — the minimum retention voltage for the RTC circuit — the laptop can no longer hold the clock value once mains power is removed. Every cold boot then pulls the clock back to a fixed default, typically January 1, 2000 or the BIOS manufacture date. This is not a BIOS fault; it is the cell failing to maintain the SRAM state. Replacing the cell and then saving the correct date and time in BIOS resolves it permanently.
CMOS checksum error on boot after the swap
A checksum error on first boot after fitting this cell means the BIOS detected that stored settings no longer match their checksum — expected behaviour when CMOS power was interrupted during the replacement. The BIOS resets all stored values to defaults and flags the mismatch. Navigate into BIOS setup, restore any custom settings, set the correct date and time, then save and exit. The error will not reappear on subsequent boots once a valid checksum is written.