Lenovo ThinkPad Edge CMOS Battery 04W0331 3V 150mAh

Lenovo ThinkPad Edge / X130e / X121e — 3V Lithium CMOS Backup Battery (04W0331)

This is a 3V lithium coin cell rated at 150mAh (0.45Wh), sourced to match OEM part number 04W0331. It fits the ThinkPad Edge, ThinkPad Edge 11, ThinkPad 13, ThinkPad X130e, ThinkPad X121e, and related models. The CMOS cell powers the RTC circuit and SRAM on the motherboard, holding BIOS settings, clock data, and boot configuration whenever mains or main battery power is absent.

• ThinkPad Edge platform fit: These models share the same motherboard RTC circuit layout and connector footprint. The 04W0331 cell uses a two-wire lead with JST-style connector rather than a bare coin cell socket, so the physical connector must match — not just the voltage.
• Bench tested on actual hardware: We measured open-circuit voltage before shipping. Every cell leaves at or above 2.95V. We confirmed the BMS handshake is not involved — this is a passive cell with no protection circuit. The motherboard reads retention voltage directly from the cell leads.
• 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 resets to a default value — typically 2000-01-01 — on any power interruption. The new cell will hold whatever value you set from that point forward.

BIOS clock resetting to year 2000 after every power cycle

The ThinkPad Edge RTC circuit requires the CMOS cell to hold above 2.8V to retain clock and settings data. Once the original cell drops below that threshold, the RTC loses state every time AC power is removed. A depleted cell can still show 2.5–2.7V on a multimeter at rest — that reads as "present" but falls below retention voltage the moment the circuit draws current. Replacing the 04W0331 cell and setting the clock in BIOS resolves this immediately.

CMOS checksum error on boot after fitting a new coin cell

A checksum error on first boot after a cell swap is normal on these ThinkPad models — it means the BIOS detected that stored values no longer match the checksum from the previous session. The cell itself is not faulty. Enter BIOS setup, verify settings, set the correct date and time, then save and exit. If the error persists on the next cold boot, check that the connector is fully seated — a partial connection causes intermittent voltage drop that triggers another checksum failure.