The Mod Shop has just released an open source project that allows you to replace the circuit board of your aging N64 Controller Pak with a more modern design that uses FRAM, which doesn’t require a battery to retain saves. At the moment, they’re not planning on selling pre-populated ones, requiring you to have the boards made, purchase the components from the listed Bill Of Materials (BOM) and solder your own. You’ll also have to either specifically order the boards with beveled edges, or attempt the painstaking and difficult process of beveling it yourself; Not doing so could potentially damage your controller.
Here’s the github with the gerbers and BOM: https://github.com/Element18592/N64-FRAM-Memory-Pak
While I’m always a fan of open source designs, this might not be for everyone, as it requires soldering surface-mount components and making the entire thing yourself. In fact, the FRAM chip alone seems to be selling between $10 and $15 from reputable sources, so just purchasing a pre-made solution like the ForeverPak 64 might be a better choice overall for most people. That said, if you’re comfortable making your own boards, this appears to be a great drop-in replacement for the originals, that will fit in any official Nintendo Controller Pak (memory card ;p).
For more information on Controller Pak’s and alternatives, check out my N64 getting started video:
I looked around and surprisingly couldn't find an open and available FRAM memory card mod for the N64, only OEM card mods and some custom designs being sold online so I made my own.
— The Mod Shop (@TheModShopCO) November 29, 2021