I modded my copy of Pokemon Gold to save games without relying on the internal save battery. I'm fairly certain this mod can be performed on most other gameboy games too.
Sorry I couldn't make a video, but you wouldn't be able to see anything because of the horrible glare on the screen. Here's a picture of the cartridge.
To do this, I desoldered the SRAM chip (the one on the bottom left), and replaced it with a non-volatile FM28V020 FRAM chip. The FM28V020 doesn't require a battery to retain it's memory, and it has the same footprint as the SRAM chip that was in the cartridge so no fancy rewiring is needed. I figured this out by accident, but in order to make this mod work, you need to lift the top right pin of the FRAM and leave it disconnected.
I have a good feeling that this would work in n64 memory cards too. It just wouldn't be multi-bank (like Kibble's non-volatile n64 memory card mod)
If you decide to do this mod, please buy the chip as opposed to ordering a sample of it. It's totally up to you, but these companies can't keep making quality products if their not making any money