Macintosh PRAM Battery Types

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Tech Tip: If you live in an area with frequent thunderstorms (especially Florida and the southeastern US) you should do everything possible to protect your system. This includes turning off the power strip or unplugging the computer EVEN if the result is a shorter PRAM battery life (see below). Also, it doesn’t do any good to have a computer on a surge suppressor or UPS if the system has an attached modem and the phone line isn’t protected by an in-line surge suppressor. For more information on this subject see "Don’t Forget to Shut the Back Door!" in the "Articles of Interest" section of the FAQs at this site. See below for sites that offer FREE on-line technical support for Apple Macintosh products.

Apple and Macintosh computers typically use a 1/2 AA, 3.6 Volt, "snap-in" Lithium battery to maintain Parameter RAM (PRAM). The first indications that the PRAM battery is failing are that the date and time are running slow or have reverted back to the BIOS initialization date (usually a date in 1956 that, coincidentally, is Steve Wozniak’s birthday) or loss of Chooser items when the system is powered on. Usually, you can reset the date, time, screen type and printer connection. In extreme cases, the system can’t access the printer or the system won’t boot at all.

There are two types of 1/2 AA batteries. They are physically identical but have different current drain characteristics. The low current drain version is used in the older series of computers including the Class, IICX, IICI, LC, Quadra, et al. The high current drain version is recommended for the Power Macintosh, Performa, et al (and clones) from the 61XX through 95XX series. Users can substitute the TL2150/S (or TL5902/S) for the TL5101/S, but not vice-versa. Later Macs (after the Power Mac 6100 series) typically use the high-current drain version. Mac clones use both the 1/2 AA 3.6 Volt Lithium and the Rayovac 840 (see table below).

Some models (Performa series, et al) use a Rayovac 840. This is a 4.5 volt alkaline battery with a wire harness and 4-pin Berg connector. This battery was used because these systems had circuitry problems and would not function properly at 3.6 Volts. The good news is that Apple provided a battery that eliminates day-to-day issues with these systems. The bad news is that the batteries don’t last as long as the Lithium batteries used in other Macintoshes. Average battery life is around two (2) years. However, some users report battery life of just over one (1) year.

The reason for lower battery life in these systems can be attributed to several factors. The first is that the Macintosh was designed to draw current from the AC outlet EVEN when powered off. If you unplug the system, manage the AC with a surge suppressor (or power strip) or are plugged into a managed power outlet, the battery stays in use and depletes more rapidly. Other things that can affect PRAM battery life are a malfunctioning power supply or a system with significant additional RAM or peripherals that cannot be supported by the original power supply.

Alkaline batteries like the Rayovac 840 can be adversely affected by the high temperatures found inside the CPU case. This is called "thermal wear-out." Yet one more thing that can affect battery life is when external peripherals like Jazz and Zip drives, Modems and FAXes are left turned on when the CPU is turned off. This apparently induces a bias condition on the system board via the serial port. The result is that the PRAM battery drains faster.

Some older Macintosh models use full size AA 3.6 Volt, "snap-in" Lithium batteries, alkaline round cells and even soldered-on devices. Resource 800 provides replacements for all of these types.

If you are not familiar with how to safely open the system case and locate the PRAM battery, visit Charles Phillips’ Macintosh Motherboard Battery Information page at . This site provides complete details on how to safely change the battery in your system along with color photos showing the location and type of battery used in each model.

840 - Rayovac 840 4.5 Volt Alkaline CMOS PRAM Battery

The Rayovac 840 is a 4.5 Volt 650 mAh alkaline computer clock CMOS PRAM battery with a 7 inch wire harness Berg-type connector and Velcro fastener. Apple part number: 922-0750. Note - the Rayovac 840 is now made using machine assembled cases. The manufacturer logo and identifying markings are embossed onto a solid plastic case. Older Rayovac 840 batteries use a paper label and have not been manufactured since 1997. The Rayovac 840 battery replaced the Rayovac 841 battery (3 inch wire harness in 2003 and can be used to replace the Rayovac 844 battery (same Voltage but lower capacity).

The Rayovac 840 battery is typically used in Macintosh Performa desktop systems plus the clones made by Motorola (StarMax and UMax) as a PRAM retention battery. Many types of IBM desktop systems including those made by Hewlett-Packard, Compaq and Dell use the Rayovac 840 battery to maintain the computer clock and CMOS RAM information. 

Note: Alkaline clock batteries including the Rayovac 840 can be shipped interstate via UPS ground or air services plus USPS Priority Mail.


Regularly: $10.00

On Sale: $6.75

The Rayovac 840 is specified for use in the following Macintosh and Mac-clone systems.  Special Note: Logic boards of the Color Classic, Macintosh LC520 and LC/Performa 550 were revised and use Apple Part Number 922-0750 (now the Rayovac 841).  You should determine which battery was used PRIOR to ordering.  The list is long so be prepared to scroll or use the "Edit (Find on this page)..." function of your Internet browser to locate the model number.