• Hello, Guest! Welcome back, and be sure to check out this post for more info about the recent service interruption and migration.

Homebrew PRAM Batteries


Well-known member
Yep, makeshift computing. When I first got my LC I immediately assumed buying such a custom battery would be impossible, so I set out to make one.


3xAAA Battery holder from LED flashlight.

3xAAA batteries. I used alkaline.

Connector and Leads from the old battery

Electrical tape

And this is how it is now:





Well-known member
Heh, I just came here to see if anyone had done something similar. I just stumbled across a Japanese page where the guy had done something similar for his 6300. My 5400 had a dead battery when I got it so I bought one from ebay to replace it. Then I left it idle for too long and that one also died. So it's been left dead ever since. I never thought about using 3xAAAs as a replacement.

BTW I was told some time ago that it's possible to remove cells from a 9v battery to make it into a 4.5v. I just did a quick google, and found this.



Host of RetroChallenge
I have 2xAA's in my IIgs, I just bought a battery holder from Radio Shack... The clock's drifted by a few minutes in the last five years (presumably due to the voltage being a tad low), but aside from that it works fine.



Well-known member
I've been trying to find a triple-AAA holder that doesn't have the batteries all side-by-side. One on top and two below is what I'd prefer. But no luck in finding one. Maybe picking up a cheap LED flashlight and pulling out the battery carriage is the best option. Though I'd prefer to have both wires connected to the one end like a regular holder.



Well-known member
Radio Shack sells battery holders which take four batteries. All you need to do is solder a wire across the space of one of the batteries. I've done this on two different motherboards:

View attachment 15855





Well-known member
Yep I think one of those flat triple holders might be better in the long run. The only thing is their footprint might be a bit big. I'll have to have a closer look inside my 5400.

At least with these you can replace the batteries without having to lift the holder (assuming you've velcro-ed it down). And there's also no danger of batteries slipping out if the plastic weakens. You can also get enclosed box holders (even some with on/off switches).



Well-known member
all the pram batteries are removed from my computers

(no battery = no leak)

i have to many computers to put a pram battery in each of them

for the fiew who need a battery to start up (macintosh II, IIx, IIfx, ..) and the ones with a bad accessible pram battery location (IIci, IIcx, ..)

i use a (or two) mono mini jack (female) at the back of the computer - hole drilled in and attached to a replacable clamp (never in the case of the computer)

and a male mono mini jack at a battery holder (different color of the mini jack for different voltage)

so i can attach effortless the 'removable pram battery' for the time needed or wished



Well-known member
the clock's drifted by a few minutes in the last five years
Consider to use the software "Clock Adjust", a small programme residing in the Control Panels folder. The software permits to set a drift to compensate for. Each time the computer boots, the programme calculates the deviation caused from the clock drift since the last boot process. The programme sets the clock to the correct time and terminates itself.


Well-known member
or if your mac is on the internet, do what I do. use a network time control panel. it sets the clock on bootup.



Well-known member
Another alternative I've seen online is to use three "button" batteries. Much smaller footprint than the AAA or AAAA batteries.


Not sure if the holders are on ebay. I found these on Yahoo Auctions in Japan. Might be a bit more expensive but tidier.



Well-known member
i like the 3 button battery idea better.

This is my opinion, but i really really really really really would NOT install the batteries on top the motherboard. if one of them goes, there goes your board. I would use an extended wire, and find somewhere else inside the mac to stick em, encase them or something.



Well-known member
I recently started soldering CR2032 battery holders into my macs. Seems to work well enough witht he compacts but I ahve not tested with the IIfx yet.


Dennis Nedry

Well-known member
The clock's drifted by a few minutes in the last five years (presumably due to the voltage being a tad low), but aside from that it works fine.
Because the clock uses a crystal, and crystals resonate based on their physical dimensions/properties, it won't slow down with low voltage. With low enough voltage, there is a point where a crystal stops resonating properly (too weak, just stops, or oscillates weird), but that causes the time to be off wildly.

So a low voltage battery shouldn't slow down your clock and a high voltage battery shouldn't speed it up.



Well-known member
well, thats because crystal oscillators drift as well. Thats why rock stable oscillators require a crystal-oven based oscillator, and the most accurate oscillator is a temperature controlled laser pumped rubidium crystal based setup, like what is on board a satellite.

This is why the advent of PLL has came along, to account for this in radio circuits, etc... But regular crystals jitter and drift during operation, and regular cheap old crystals are only accurate to roughly 100ppm.