All PS/2s use a battery, to power the CMOS memory that holds configuration information, and to run the internal date-and-time clock. This page summarises the different kinds of batteries in use, and gives the occasional hint on obtaining or fitting them.

Machines use batteries as follows; click on the FRU number for more information on that particular item:

FRU 33F8354

This is a conventional coin-shaped 3 volt lithium cell; typical cost is about $3-$5. Equivalents are:

FRU 64F9987

This consists of two conventional coin-shaped 3 volt lithium cells soldered to a small circuit board, attached to a 5cm 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.

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. Cost is around $15. [thanks to Louis Ohland for this bit]

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

FRU 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; typical cost is about $10-$15. Equivalents are:

FRU 8509237

This is a Dallas self-contained CMOS RAM module with integral real-time clock 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.

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.

Typical cost is $10-$15. Equivalents are: