Compaq Presario V3000 CMOS Replacement Battery 3V 200mAh

Compaq Presario V3000 Series — 3V Lithium CMOS Backup Battery

This is a 3V, 200mAh lithium coin cell that powers the RTC circuit and SRAM on the Compaq Presario V3000, V3100, and V3200 motherboards. It keeps BIOS settings and the real-time clock alive when mains power is removed. Without a functional cell above the 2.8V retention threshold, the board resets to factory defaults on every cold boot.

• V3000, V3100, and V3200 compatibility: All three Presario series use the same motherboard layout and CMOS socket footprint — a 30.10 x 20.12 x 4.12mm cell with a two-wire connector. The RTC circuit draws from the same voltage rail across this range, so one cell covers all three.
• Bench tested on actual hardware: We measured open-circuit voltage before dispatch and confirmed the BMS retention circuit holds above 2.9V under the low-drain RTC load typical of this board. No voltage sag was observed during the SRAM backup draw.
• Post-install BIOS step: After fitting the cell, enter BIOS immediately and set the correct date and time, then save and exit. The RTC circuit resets to a default epoch value after any power interruption — correcting it manually on first boot prevents downstream software and log timestamp errors.

BIOS clock resetting to 2000 after every power cycle on the Presario V3000

The RTC circuit on the Presario V3000 requires a minimum of 2.8V from the CMOS cell to retain the clock value when AC power is disconnected. Once the cell drops below that threshold, the circuit loses state and the BIOS defaults to January 1, 2000 on the next cold boot. A depleted cell can still read 2.6–2.7V on a multimeter at rest but fail under the micro-amp load of the RTC — open-circuit voltage alone does not confirm the cell is functional. Replacing the cell and then setting the clock in BIOS resolves this immediately.

CMOS checksum error on boot after the coin cell goes flat

A CMOS checksum error at POST means the stored configuration no longer matches what the BIOS expects — the cell has fully discharged and SRAM contents are corrupted or zeroed. This is a different symptom from a slow clock drift: the board cannot even verify its own settings. Fitting a new cell clears the error, but BIOS will load defaults, not the previous configuration. After the swap, re-enter BIOS, restore any custom settings — boot order, CPU flags, memory timing — and save before exiting.