gman_modz on eBay is selling a new from-scratch FRAM based N64 Memory Pak. FRAM does not require a save battery and is a rugged replacement that shouldn’t lose saves. The Paks come with a 3D printed shell, or the PCB fits an original N64 Memory Pak as a drop-in replacement. They cost $28 + S&H.
GMANMODZ documents the process of creating the new boards on their blog.
Source: https://gmanmodz.com/2021/01/22/n64-memory-pak-from-scratch/
Purchase: https://www.ebay.com/itm/Nintendo-N64-Controller-Memory-Pak-FRAM/254823249194
Nintendo 64 System – Video Game Console (Renewed)
$132.95
(as of December 10, 2023 02:46 GMT -05:00 – More infoProduct prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on [relevant Amazon Site(s), as applicable] at the time of purchase will apply to the purchase of this product.)