Common issues with Apple Macintosh Systems – Part 2 : PRAM Batteries

Welcome to Jason’s Macintosh Museum!

This video is all about batteries – specifically, the Parameter RAM (PRAM) batteries that live inside every Apple Macintosh system.

There were three main types of PRAM battery that Apple used on their Macintosh systems:

1984 – 1987 : A21PX (AA size, 4.5V Alkaline)
1987 – mid 2000s : (1/2 AA size, 3.6V Lithium)
1994 – 1998 : (4.5V Alkaline, plastic case with leads)

If any of these are left inside a system for an extended period of time, these batteries can start to leak, and the battery acid can corrode the logic board, rendering it useless. Therefore, you should never leave the PRAM batteries inside any system unless you have one of the specific systems that need one to boot.

For example, the Macintosh II, IIx and IIfx all need two working PRAM batteries to boot, so that the power supply control circuitry on the logic board can function and start up the main power supply unit.

Some other systems (such as the LC 475), require a PRAM battery to be present in order for the system to boot and initialise the video.

I personally have several systems that have been rendered useless by leaking batteries (IIfx, PowerMac 8100, PowerBook 190), and I hope this video will clearly show the risks involved in leaving a PRAM battery inside an old Apple Macintosh system.

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Source by Jason’s Macintosh Museum