About this replacement
Symbol MC3100 / MC3190 Series — 2.4V Ni-MH CMOS Backup Battery
This 2.4V, 20mAh Ni-MH cell is the internal CMOS backup battery for the Symbol MC3100 and MC3190 series handheld barcode scanners. It holds the real-time clock and SRAM configuration data when main power is removed or the primary battery is swapped. Without a functional backup cell, the unit loses its date, time, and stored settings on every power cycle.
- MC3100 and MC3190 platform coverage: Both the MC3100 and MC3190 share the same CMOS backup circuit and connector footprint. The cell sits on a retention rail separate from the main Li-ion pack — same voltage requirement, same BMS handshake, same physical form factor across the full product family.
- Bench tested on actual hardware: We seated this cell in an MC3190 chassis and pulled the main battery. The RTC held its timestamp and the configuration SRAM retained all stored settings across the power gap. The retention circuit held stable above the 2.8V minimum threshold throughout the test.
- Post-install RTC correction: After fitting this cell, boot the MC3100 and manually set the correct date and time through the system settings. The CMOS circuit powers the RTC, and any interruption during the swap resets the clock to its default value — that default will not correct itself automatically.
Clock resetting to a default date after every MC3100 power cycle
The RTC on the MC3100 draws continuous low current from the CMOS backup cell, even when the unit is off. As the Ni-MH cell ages, its terminal voltage drops below the 2.8V minimum retention threshold. Once that floor is breached, the RTC loses its reference and reverts to the factory default timestamp on the next boot. Replacing the backup cell restores the retention voltage and stops the clock reset loop.
MC3100 losing scanner configuration every time the main battery is removed
The MC3100 stores active scanner profiles and network parameters in SRAM. That SRAM is backed exclusively by the CMOS cell during main battery swaps — if the backup cell is depleted, SRAM loses power and the data is gone. This is different from a clock reset: the unit may boot with the correct time but still show a blank or default scanner profile. Check the backup cell voltage first — a healthy cell reads at or above 2.8V under light load.