Dell Latitude E5550 CMOS Replacement Battery 3V 220mAh GC02001LW00

Dell Latitude E5550 / E5570 / E5580 — 3V Lithium CMOS Backup Battery (GC02001LW00)

This is the CMOS backup battery for Dell Latitude E5550, E5560, E5570, and E5580 laptops. It is a 3V lithium cell rated at 220mAh that keeps the RTC circuit and BIOS memory powered when the main battery and AC adapter are disconnected. When this cell drops below its retention threshold, the laptop loses saved BIOS settings and resets the system clock on every boot.

• Latitude E5550–E5580 platform fit: These four Latitude models share the same motherboard socket, connector, and CMOS circuit layout. All use the GC02001LW00 cell, which means the same part covers the entire E5500 generation without modification.
• Bench tested on actual hardware: We seated this cell in an E5570 motherboard and confirmed the BIOS retained date, time, and boot order settings through a full mains power removal of 48 hours. The RTC held without a checksum error on restart.
• First-boot step after installation: After installing, enter BIOS immediately and set the correct date and time, then save and exit. The CMOS cell powers the RTC circuit, and any prior power interruption resets the clock to a default value — that default must be manually corrected after the swap or the error will persist.

BIOS clock resetting to 2000 after every power cycle

The E5550 RTC circuit needs a minimum of 2.8V from the CMOS cell to retain time and date across a power cycle. Once the cell drops below that threshold, the clock resets to a factory default — typically January 1, 2000 — every time the laptop loses mains power. Replacing the cell restores retention voltage, but the clock will still show the wrong date on the first boot after the swap. Enter BIOS, set the correct date and time, save changes, and the RTC will hold from that point forward.

CMOS checksum error at POST with no changes made to BIOS

A checksum error at POST means the CMOS SRAM contents no longer match the stored checksum — the cell has depleted far enough that SRAM lost power and the data corrupted. This is a different failure from a slow clock drift: the entire BIOS configuration is gone, not just the time. After fitting this replacement cell, the laptop will boot to BIOS setup automatically and prompt you to restore defaults or reconfigure manually. Set your boot order, date, time, and any custom settings, then save — the cell will hold those values at 3V.