Casio IT3000 CMOS Replacement Battery 3V 200mAh Lithium

Casio IT3000 / IT3100 / IT3000m53e — 3V Lithium CMOS Backup Battery

This is a 3V, 200mAh lithium coin cell that replaces the CMOS backup battery in the Casio IT3000 series mobile handheld terminals. It fits the IT3000, IT3100, and IT3000m53e. Its sole job is to hold RTC clock values and SRAM-backed settings when the main battery is removed or depleted.

• IT3000, IT3100, and IT3000m53e compatibility: These three models share the same motherboard layout and CMOS retention circuit. The RTC and SRAM both draw from this cell when main power drops. One cell covers all three variants.
• Bench tested on actual hardware: We verified open-circuit voltage at 3.0V and confirmed the cell holds retention voltage above the 2.8V minimum threshold that the IT3000 CMOS circuit requires to preserve settings across a main power disconnect.
• Post-installation clock correction: After swapping the cell, power the unit on and manually set the correct date and time — the RTC resets to a default value the moment the old cell is removed. Save the settings before powering off, or the clock will appear wrong on next boot even with a good cell installed.

Clock resetting to a default date after every power cycle on the IT3000

The IT3000 RTC circuit draws exclusively from the CMOS coin cell whenever the main battery is absent or below operational voltage. Once the coin cell drops under 2.8V, it can no longer sustain the RTC register values through a power gap. The clock resets to a factory default — typically January 1, 2000 — on every cold start. Replacing the coin cell and then manually entering the correct date and time through the device settings is the fix.

CMOS checksum error on boot after the IT3000 sat unused

A checksum error means the CMOS data the device reads at boot no longer matches what was stored — a sign the cell has dropped below the minimum retention voltage and allowed the SRAM contents to corrupt. This happens most often after the unit sits in storage for months with no main battery installed. The coin cell self-discharges during storage and eventually loses the ability to hold register values at all. Fit a fresh cell, clear the CMOS if the device prompts you, and re-enter all configuration settings from scratch.