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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.


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.

As for fixing a low/dead battery in the DS1287, see here.