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PS/2 RTC/CMOS Batteries

Overview
6 V Lithium Battery Pack
Dallas RTC/CMOS Module
Dallas 2 KB NVRAM Module
3 V Coin Cell Battery
Dual Coin Cell Battery Pack
3 V Lithium Through-Hole Battery

Based on content by Bob Eager (original) and Peter H. Wendt (original). Edited by Major Tom.

Overview

All PS/2s (except for Model 25 8086) use a battery of some kind to power the CMOS memory that holds the system configuration information, and to run the Real Time Clock (RTC). This page lists the different kinds of batteries in use and what their modern alternatives are. Provided are also some tips on removing and reinstalling the battery.

Cross-reference of individual PS/2 Models and the corresponding battery types. Click on the FRU number for more information on that particular item:

6 V Lithium Battery Pack

FRU P/N 72X8498

This is a 6 volt two-cell lithium pack. The original IBM ones are usually yellow, with black ends. Replacements are available as camera batteries. Equivalents are:

The battery is held in a special Battery/Speaker Assembly.

Dallas RTC/CMOS Module

FRU P/N 8509237

This is the infamous self-contained Dallas CMOS RAM module with an integrated RTC/CMOS chip and battery. The entire module must be replaced. The Dallas part number is DS1287, but this part is now obsolete. According to the Dallas Semiconductor data book, the DS1287 can be replaced by the DS12887 (the latter is pin compatible but has more RAM).

The DS12887 is not Year 2000 compliant, but of course PS/2s are compliant except that a manual reset of the date is required at the start of the year 2000. Do NOT be tempted to use the Year 2000 compliant upgrade to the DS12887, which is designated the DS12C887; it uses the century byte differently to a PS/2 and will apparently not work.

A lead free/ROHS compliant version of the DS12887 part is the DS12887+, which works perfectly well in a PS/2.

The DS1287 can also be replaced by the DS1287A, and the DS12887 by the DS12887A; the only difference in each case is that the part with the 'A' suffix has a pin which can be used to clear the RAM; this pin is unused on PS/2s.

Equivalents are:

Some useful info about DS1287 and other RTC modules can be found HERE.

There is also a way to Rework the DS1287 (by attaching an external battery to the RTC module).

Dallas 2 KB NVRAM Module

FRU P/N 64F0722

This is another self-contained Dallas module. This one integrates 2 KB of NVRAM and a battery (no RTC). The entire module must be replaced. The Dallas part number is DS1220AD.

A lead free/ROHS compliant version of the DS1220AD part is the DS1220AD+, which works perfectly well in a PS/2. This part is still active.

Equivalents are:

3 V Coin Cell Battery

This is a conventional 3 V lithium coin cell battery (20 mm x 3.2 mm). Equivalents are:

Battery Voltage and Life Expectancy

The battery used on the 95xx products has a normal life expectancy of five to seven years. The life of the battery is directly related to how the machine is used. Battery voltage is consumed only when the system is powered off. Since the battery is a lithium battery, it has very long shelf life. For correct machine operation the battery voltage should be between 2.5 volts and 3.7 volts.

Note: Low voltages can corrupt CMOS bits.

To check the battery voltage:

• Turn off the system unit power.
• Remove the battery from the battery holder.
• Check the battery for a voltage of 2.5 - 3.7 V DC

If the battery voltage drops below 2.5 volts, it should be replaced with FRU P/N 33F8354 (CR2032). After replacing the battery, the system unit should be powered on and checked for proper operation.

Dual Coin Cell Battery Pack

FRU P/N 64F9987

This consists of two conventional coin-shaped 3 volt lithium cells soldered to a small circuit board, attached to a 5 cm red & black cable with a battery connector at the other end. A plastic hood covers the two cells. Currently, there is no known direct equivalent.

The lithium cells are 3 volt coin cells with two solder tags on one side. Equivalents are:

These cells are not as easy to find as any of the others listed here; places to try include:

• Action Electronics
• Batteries Plus
• TechAmerica
• WatchBattery (in the UK)

An alternate approach is to use an AT-style battery pack, or anything else that will fit inside the case! AT replacement battery packs are rated at 6.0 volts, and generally contain a resistor which prevents charging and controls the voltage. They come with attached wires, a 4 pin connector and velcro mount, and fit nicely in the battery/speaker cavity. The velcro can be used to attach it to the bottom surface so that it doesn't move. The header pinout is correct, and even has the plug in the second hole to correctly polarize the header.

One source is the BR-E3-BP, from Batteries Plus.

3 V Lithium Through-Hole Battery

There is no FRU P/N for the battery itself. It is soldered in place and was to be replaced with the entire riser board.

This is a 2/3A (17 x 33.5 mm) cylindrical 3 V lithium battery with solder tabs. There are different variants of the battery - for a direct replacement you need one with a single-pin (-) tab and a two-pin (+) tab.

Alternatively, you can replace it with a AA battery holders rated for 3 V. They come with attached wires (red for + and black for -) and velcro mount to put them i.e. at the rear of the unit or somewhere else.

A 2/3A battery holder called BH2/3A can also be used. However, you will have to compensate for the different pin arrangement (two single-pin terminals) if you want to solder it directly to the riser.