Parent

Compaq Portable III  -  CMOS battery options

NOTE:

Compaq Portable III,  not the Compaq Portable 386.

OPTION #1

1.  Low profile 4-terminal non-rechargeable battery module (3.4V battery with diode and resistor) soldered to the motherboard.  Part number 107157-001
2.  Supporting components for the battery module: Diodes + resistors + transistor
3.  MC146818 CMOS/RTC chip in IC socket U77
4.  Supporting components for MC146818: Crystal + MC14069 chip + capacitors + resistors

The battery module powers the MC146818 when the computer is powered off.

Photo at here.

The second photo in post #6 at here shows how someone substituted a 3.6V lithium battery in place of the battery module.

At here is shown a third party replacement.


OPTION #2

1.  No battery module
2.  Dallas DS1287 CMOS/RTC module (contains a battery) in IC socket U77
2.  Zero-ohm links

The battery in the DS1287 powers the DS1287 when the computer is powered off.

Photo at here.

DS1287 modules are no longer made.  DS1287 modules, found on eBay and elsewhere, possibly contain a dead (or well depleted) battery.  Note that per here, a DS12887 is not always a replacement for the DS1287.

See here for guidance on bypassing the low/dead battery in the DS1287 module.