Brother Fax4100e CMOS Backup Compatible Battery 3.6V 450mAh

Brother Fax4100e Fax Machine — 3.6V Ni-MH Replacement Battery (3/V450HR)

This is a 3.6V, 450mAh Ni-MH CMOS backup battery for the Brother Fax4100e Fax Machine. It replaces OEM part 3/V450HR and sits on the main board, powering the SRAM and RTC circuits when mains power is removed. When this cell depletes, the machine loses stored phone numbers, transmission logs, and settings every time it's unplugged.

• Fax4100e memory retention circuit: The Fax4100e uses a dedicated Ni-MH backup cell — not a standard coin cell — because the SRAM and RTC together draw more sustained current than a CR2032 can supply. The 3/V450HR cell holds a minimum retention voltage above the 2.8V threshold required to keep SRAM content valid during mains outages.
• Bench tested on actual hardware: We cycled this cell through repeated mains-disconnect events on a Fax4100e board and confirmed the BMS held retention voltage without resetting the RTC or clearing stored directory entries.
• After installation on the Fax4100e: Once the new cell is installed and the machine is powered on, manually re-enter the date, time, and station ID through the machine's menu — the RTC defaults to a factory timestamp after any cell swap and must be corrected before the machine logs transmissions with accurate timestamps.

Settings lost every time the Fax4100e is unplugged

The Fax4100e stores phone book entries, speed-dial numbers, and fax settings in SRAM. That SRAM is powered exclusively by the backup cell when mains is removed. Once the cell drops below approximately 2.8V, the SRAM loses power and all stored data clears. A depleted cell may still show some voltage on a multimeter — testing under load is the only reliable way to confirm it has failed. Replacing the 3/V450HR cell and re-entering settings through the machine's function menu resolves this.

CMOS checksum error and clock reset to default date on the Fax4100e

A checksum error on boot means the machine has detected that its stored configuration no longer matches what the CMOS circuit last recorded — typically because the backup cell is completely flat and the SRAM cleared. The RTC simultaneously resets to a fixed factory default timestamp. This is a different symptom from intermittent data loss: here, the machine flags the corruption directly at startup rather than failing silently. Fitting a new 3/V450HR cell, then setting the correct date and time through the Fax4100e's initial setup menu, clears the error and restores normal logging.