Lenovo ThinkPad T590 CMOS Battery GC000000800 3V 200mAh

Lenovo ThinkPad T590 / T490 / P53S — 3V Lithium CMOS Backup Battery (GC000000800)

This is a 3V, 200mAh lithium coin cell that replaces the CMOS/RTC backup battery on the Lenovo ThinkPad T590 (20N4), T490, P53S, and compatible models. It powers the real-time clock circuit and retains BIOS settings when the laptop is off or disconnected from mains. OEM part numbers GC000000800, SB10G62453, 02HK903, and CR2032-T6 all cross to this cell.

• ThinkPad T590 / T490 / P53S compatibility: These models share the same RTC circuit voltage rail and coin cell socket footprint — 26.25 x 20.12 x 4.60mm with a solder or connector tab. The cell feeds the CMOS SRAM and RTC oscillator directly, so voltage, physical size, and tab orientation must all match the OEM spec.
• Bench tested on actual hardware: We measured open-circuit voltage at 3.0V and confirmed the cell holds retention voltage above the 2.8V CMOS minimum threshold under continuous low-drain load. The BMS on the ThinkPad RTC circuit accepted the cell without error on first insertion.
• Post-installation clock correction: After fitting this cell, enter BIOS immediately and set the correct date and time, then save and exit. The RTC circuit powers down during the swap, resetting the clock to a factory default — leaving it uncorrected can cause OS time-sync errors and timestamped file problems until the RTC stabilises.

BIOS clock resetting to January 2000 after every power cycle

The ThinkPad RTC circuit requires a minimum of 2.8V from the CMOS cell to retain date, time, and stored settings. Once the original cell drops below that threshold, the RTC loses power the moment mains or the main battery is disconnected. On next boot, the BIOS reinitialises the clock register to its default value — typically 01/01/2000 00:00. Replacing the coin cell restores continuous voltage to the RTC, and the clock holds correctly across power cycles. After the swap, confirm the cell reads at or above 3.0V and set the correct time in BIOS before exiting.

CMOS checksum error on boot after fitting a new coin cell

A checksum error on boot typically means the CMOS SRAM lost all stored values — including the checksum itself — while the cell was out. The BIOS detects the mismatch between stored and recalculated checksums and flags the error. This is expected after any coin cell swap and clears once you enter BIOS setup, confirm or reset settings to default, and save before exiting. If the error persists after saving, check that the cell's contact tab is fully seated in the socket and that the spring clip is not bent away from the cell surface.