Simion32 wrote:I don't remember which battery the cart takes (was it CR2016?).
Many sources say CR2032.
WesternTanager, It may benefit you to get a battery with pre-soldered tabs. Either way, there will still be some soldering to be done, but that's one less step you'll have to do. Note: I'm
not speaking from experience, as I haven't soldered a single thing in my life...
The only cart-based game with battery-backed memory I've played lately was DK64, a few months ago. At the risk of jinxing myself, that battery still worked after around 23 years, and I managed to complete the game over the course of a couple of weeks.
The oldest cart with battery backup I have is Kirby's Adventure for NES, which first released in 1993 (I have games that first released before this with battery backup, but I'm not sure how long those sat on store shelves/in inventory before my family purchased them in 1994. They don't have Player's Choice Million Seller labels).
My Memory Paks (which were third-party versions) all stopped reliably retaining data after a year or so of owning them, and the first one was even purchased brand new!