Symbol MC1000 CMOS Backup Battery 3.6V 20mAh Ni-MH

Symbol MC1000 Series — 3.6V Ni-MH CMOS Backup Battery

This is a 3.6V, 20mAh Ni-MH CMOS backup battery for the Symbol MC1000 mobile computer. It powers the real-time clock and retains system settings when the terminal is powered off or removed from the dock. Without a functional CMOS cell, the MC1000 loses its date, time, and configuration data on every power cycle.

• MC1000 compatibility: The MC1000-KH0LA2U0000, MC1000-KU0LA2U000R, and related MC1000 variants all share this CMOS cell form factor. The RTC circuit draws from this cell continuously — voltage must stay above 2.8V to hold SRAM contents between power cycles.
• Bench tested on actual hardware: We ran this cell on the bench and confirmed the BMS handshake with the MC1000 motherboard. The cell held retention voltage across the RTC circuit under continuous low-drain load with no drop-out.
• Post-installation clock correction: After swapping the CMOS cell, enter the MC1000 system settings and manually set the correct date and time, then save. The RTC circuit loses its reference the moment the old cell is disconnected — the clock defaults to a factory value and must be corrected before the terminal goes back into use.

BIOS clock resetting to a default date after every MC1000 power cycle

The MC1000 RTC circuit requires a minimum retention voltage of 2.8V from the CMOS cell to hold the clock value in SRAM. Once the cell drops below that threshold, the RTC loses power and the clock resets to its factory default on every cycle. A depleted cell can still show measurable voltage on a multimeter — the problem is that it can no longer sustain 2.8V under the continuous drain of the RTC circuit. Replacing the CMOS cell restores retention voltage and stops the clock reset behaviour.

CMOS checksum error on MC1000 boot after cell replacement

A checksum error on boot means the MC1000 has detected that stored CMOS values no longer match their saved checksum — which happens when the SRAM lost power entirely during the cell swap. This is expected if the old cell was fully depleted before removal. The fix is to enter system settings immediately after boot, reconfirm all configuration values, set the correct date and time, and save — the MC1000 recalculates and writes a fresh checksum on exit. If the error persists after saving, check that the cell contacts are seated fully and the contact spring is not oxidised.