A quick Mac battery replacement

I attempted to power up my RackMac TZ today after not using it for several months. The system was dead - nothing. Disappointed, I removed the battery for inspection:

Battery replacement - not enough
1.52v was definitely low for this 4.5v battery, and certainly low enough to prevent the computer from booting up. Nonetheless, I still wondered about the potential for other problems and was loathe to order an expensive replacement battery that would take days to get here.

There was only one thing to do...
Battery replacement - snip

Battery replacement - base
4.5v is three AA batteries, so I dug this battery holder out of the trash (it was part of a cheap light) and broke the frame down to size.

Battery replacement - solder
Next, I soldered the dead battery's cable to the holder's sockets. Red goes to positive. This case holds four batteries, so I bridged the last battery slot with a wire.

I took the velcro off the old battery and glued it to the back of my new holder.

Battery replacement - finished
Next I installed batteries and checked the voltage. It was 4.73v, so I hooked the unit up to the RackMac. Everything works perfectly.

The official battery for these units is supposed to last several years. I have no idea how these AA's will do long-term, but I'll report back when they die.

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Tarmas's picture

if you have a mac with a 3.6 V battery just use 2 AA batteries. those .6 V don't make that much difference.

tmtomh's picture

I agree that many Macs with 3.6V batteries will function with two 1.5V batteries (for a total of 3V). However, it has been my experience that 3V is borderline for such Macs. If the voltage drops just a little, symptoms may start to show up -- perhaps not a stopped system clock but, more annoyingly, a lack of video upon startup in certain machines (LC 475/Quadra 605, pizza box PPCs, etc.)

If purchased as part of a larger order -- so shipping costs don't become an issue -- brand new 3.6V lithium batteries can be had for $5.29 from Cyberguys and elsewhere. For just $3 more than two regular AAs, I prefer to get the original type and voltage of battery.

Of course, for emergencies or for fun hacking, two AAs can work...


Tarmas's picture

I have a 3 V 1/2 AA battery in my Performa 475 for more than a year now. They're much cheaper than 3.6 V bateries. It works like a charm, though it's slightly longer than the original battery, so you have to use some force to stick it into the battery cage. The computer is off most of the time, I just switch it on like once a month to check 72-pin RAM SIMMs and I had no trouble yet. I guess that people should have no problems with a 3 V battery or a set of 2 1.5 V AA for a reasonable period of time as long as they're using alkaline batteries.

MacTrash_1's picture

There is another good alternative for 4.5v PRAM batteries. You can take an Energizer 9v battery apart and there are 6 small battery cylinders inside. You can use 3 of the cylinders to make a 4.5v battery. Solder some jumper wires across the different connectors and you have a 4.5volt battery. Then just connect your old battery wires to the battery's remaining + & - to complete the battery.

You'll need to do a little soldering and put a velcro strip on to hold the batteries together. It takes a few minutes to make one but it's better than giving Radio Shack 15 bucks for a battery.


This trick works quite nicely, and in fact, I have been using it in an entire SCHOOL of Macs (both 68K and ppc, from 575's to 5200 , 5500's, and 6400's and more) since 1996!

There is an even easier way, though, which allows you to replace the cells "on the fly," without even opening the Mac.

Use the little rectangular 4-AA holder from Radio Shack (stock number 270-391, for $ 1.39 in the 2000 catalogue). You will still need to solder a bridge to be able to use 3 cells. Now, the same technique can actually have that little holder OUTBOARD to the Mac! The two thin wires from the "recycled" battery can be carefully routed and "caught through" the rear metal and plastic covers, with no parts bent, loosened, or otherwise compromised. The holder can hang free, be otherwise supported, or even held against the rear of the Mac by the usual tangle of cables, etc.. You could, of course, use Velcro, but why bother?

How long will the batteries last? The batteries, using three regular Energizer AA alkalines, will last for YEARS! I have often gotten two years where I had forgotten a particular computer. However, if you aren't sure, or if you worry a lot at night, simply replace the three AA's every year on your birthday.

This way, no over or undervoltages, no Velcro, no muss, no fuss, and if you do the replacing of the cells while the Mac is running, you don't even have to reset the clock, etc.