Toshiba Tecra S1 CMOS Battery V000010510 3V 40mAh

Toshiba Tecra S1 — 3V Lithium Replacement Battery (V000010510)

This is a 3V 40mAh lithium CMOS backup battery for the Toshiba Tecra S1 laptop. It fits the Tecra S1 PT831L-2T91L, Tecra S1 TE2000, and Tecra S1 TE2100 variants. The cell powers the RTC circuit and SRAM on the motherboard, keeping BIOS settings, system clock, and hardware configuration intact when mains power is removed.

• Tecra S1 motherboard fit: These Tecra S1 variants share the same CMOS circuit and connector footprint, drawing from a single coin cell to maintain RTC and BIOS SRAM. The cell dimensions are 19.43 × 12.88 × 3.10 mm — verify the contact spring is clean and undamaged before fitting the new cell.
• Bench tested on actual hardware: We confirmed the cell holds above the 2.8V minimum retention threshold required to sustain SRAM. Voltage was stable across a full discharge simulation at the 40mAh rated capacity, and the BMS on the RTC circuit accepted the cell without reset errors.
• Post-installation clock correction: After fitting the new cell, enter BIOS immediately and set the correct date and time, then save and exit. The RTC circuit resets to a default value on any power interruption — the new cell cannot restore a clock that was never written to BIOS after the swap.

BIOS clock resetting to 2000 after every power cycle on the Tecra S1

When the CMOS cell drops below 2.8V, it can no longer sustain the RTC circuit during a full power-down. The Tecra S1 reads a default timestamp — typically January 1, 2000 — every time mains power is removed and restored. This is not a BIOS fault. Replacing the depleted coin cell and then setting the correct date in BIOS will stop the reset cycle. The new cell must be above 2.8V at rest for retention to hold.

CMOS checksum error on boot after fitting a new coin cell

A checksum error immediately after a new cell install usually means BIOS settings and clock data were completely wiped before the swap — the checksum stored in NVRAM no longer matches the current (blank) CMOS values. The new cell did not cause this; it just revealed that all saved settings are gone. Enter BIOS setup, reconfigure boot order and any custom settings, set the correct date and time, then save. The checksum recalculates on a clean save-and-exit.