Macintosh 128K/512K/512KE/Plus battery replacement

thingiverse

The early Apple Macintosh models (128K, 512K, 512Ke and Plus) use a special battery for the parameter RAM (PRAM). The original is a 4.5v Eveready No. 523. A compatible model (Exell A21PX) is still available, but expensive. This is an adapter that fits three generic LR44 batteries (3x1,5V = 4,5V) in series into the space of the original battery. The downside is that the capacity is only about half of the original battery (A21PX is rated 600mAh, while three LR44 sums up only at 330mAh). This means that the battery will not last as long as the real thing, but perhaps you just want to run it while setting the machine up (making sure the file dates show up right) so this will make a temporary measure. You need to add a battery contact of some sort, and a piece of wire that runs thrue the barrel to the other end. I used a piece of metal, small washer and just a piece of wire on the other end. There is a small cut where you can bend the wire's end over. The top of the battery-pile will make for the positive contact. Use three LR44s with the positive side towards the end with the opening. Negative side goes thrue the added wire to the other end of the barrel. Mount the whole thing into the Mac's battery holder, positive is down! (Please always make sure to remove any batteries from old Macs before storing the machines for a longer time! While almost any battery can leak, perhaps the LR44s won't be as likely to do that, or cause as much damage as the originals can when they leak). [More about the batteries in the early Mac](https://macgui.com/news/article.php?t=439) on MacGUI.com.