Lenovo ThinkPad X100E CMOS Replacement Battery 93P4905 3V

Lenovo ThinkPad X100e Series — 3V Lithium Replacement Battery (93P4905)

This is a 3V, 150mAh lithium CMOS cell for the Lenovo ThinkPad X100e laptop. It sits on the motherboard and keeps the RTC circuit and BIOS SRAM powered when mains and main battery are both removed. When this cell drops below the 2.8V retention threshold, the system loses its clock and stored settings.

• ThinkPad X100e 2876, 3506, 3507 compatibility: These variants share the same motherboard footprint and connector for the CMOS cell. The RTC circuit draws from this single cell across all listed models, so one part number covers the full range.
• Bench tested on actual hardware: We measured open-circuit voltage before installation and confirmed retention voltage held above 2.9V under the SRAM standby load. The BMS on the X100e motherboard accepted the cell without a checksum error on first POST.
• 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 factory default date on every swap — the new cell will hold that value, but only after you write the correct time to the RTC register.

BIOS clock resetting to 2000 after every power cycle on the X100e

The X100e RTC circuit runs entirely off this coin cell when the laptop is unplugged and the main battery is out. Once the cell drops below 2.8V, the RTC loses power and resets to a default timestamp — typically January 1, 2000 — on the next boot. A failing cell can still pass a voltage check under no load but collapse immediately under the microamp draw of the SRAM. Replacing the cell and writing the correct time in BIOS is the complete fix.

CMOS checksum error appearing on boot after fitting a new coin cell

A checksum error on first boot after a swap usually means the CMOS SRAM lost all stored values during the swap — not that the new cell is faulty. The motherboard computes a checksum over stored BIOS settings at shutdown; if those settings were wiped mid-swap, the checksum will not match on the next POST. Enter BIOS, reload defaults, set the correct date and time, then save and exit to write a fresh checksum. If the error persists on the following boot, check that the coin cell connector spring is making firm contact — oxidised or bent contacts on the X100e socket can cause intermittent voltage drop.