I still don't have a way to back up N64 carts, though I really should, but I do at least have a Dexdrive. I have one that doesn't work but I got it that way, all of my others still work fine. I've had no issues with regular Performance memory cards, though. Do make sure to get regular Performance Memory Cards and not the Pro ones, though - the Pro cards are a 4X card which uses compression to fit four memory card spots into one, and as a result are less reliable. It's crazy that a third party (Interact/Performance) actually used battery clips, something Nintendo never did, but it's fantastic for preservation purposes. Presto, the pak's good for another decade or two! Of course you'll need to back up the save files beforehand somehow, but I love these because of those battery clips.
Just unscrew the card, it uses normal Phillips screws, pull out the battery, and put in a new one. For controller paks, for anyone like me who still hasn't gotten around to teaching themselves how to solder, look up Performance's memory cards for the N64! They are those oversized cards that are about twice as tall as a Nintendo controller pak, but unlike Nintendo use a battery holder inside for the battery.
