HP Presario F502 CMOS Replacement Battery 3V 200mAh 431436-001

HP Presario F502 Series — 3V Lithium Replacement Battery (431436-001)

This is a 3V, 200mAh lithium CMOS backup battery for the HP Presario F502, F503, F505, F506, and 13 additional Presario models. It powers the RTC circuit and SRAM on the motherboard, keeping system time, date, and BIOS settings intact when mains power is removed. Without a functioning cell, those settings reset every time the laptop loses power.

• Presario F500 series motherboard fit: These models share the same motherboard socket and RTC circuit layout. The connector and cell dimensions match the 431436-001 spec directly — no adapter or modification needed.
• Bench tested on actual hardware: We measured open-circuit voltage before shipping. Each cell holds above 2.9V at rest, confirming the lithium chemistry is active and the retention voltage exceeds the 2.8V minimum the CMOS circuit requires to hold SRAM contents.
• 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 resets to a default value — often January 2000 — after any power interruption, and it will not self-correct. One manual entry after the swap is all it takes.

BIOS clock resetting to 2000 after every power cycle

The RTC circuit on the Presario F500 series motherboard draws a continuous low current from the CMOS cell to hold the clock register and SRAM contents. When cell voltage drops below 2.8V, the circuit can no longer maintain those values across a power cycle. The clock falls back to its hardcoded default — typically 01/01/2000 — on every cold boot. Replacing the cell restores retention voltage, and a single BIOS date entry after the swap stops the reset loop.

CMOS checksum error on boot after fitting a new coin cell

A checksum error immediately after installing a new cell usually means the BIOS compared stored settings against what it found in SRAM and detected a mismatch — not a faulty cell. The previous cell was depleted long enough that all SRAM contents were lost before the swap. Enter BIOS setup, confirm or re-enter your settings, then save and exit. The checksum will recalculate against the newly written values and the error will not return.