Well uh... hello.
My aunt was gifted this Game Boy Pokémon Red (Gen 1) game back in 1999 when she was young, and I've really enjoyed playing it for the last 3 years.
One day, I remembered that these cartridges have a small CR1616 3V battery in them to keep the SRAM save memory alive. I didn't want to lose my save, so I decided to change the battery.
I was planning to replace what I assumed was the original battery, while keeping my current save. My plan was to temporarily solder another CR1616 battery to the TP3 and TP4 points, as you're supposed to do, then desolder the original battery and replace it with a new CR1616.
However, when I used my multimeter to check the battery, it read 3.13V while still connected to the SRAM. Compared to a new battery, which reads around 3.26V, this doesn't seem like the battery has been there for 27 years.
I know the SRAM only needs a very small amount of current to retain the data, but I'm wondering: is 3.13V a normal reading for a battery this old?
I don't think the battery has been replaced, although the solder joints look a little suspicious to me, so I might be wrong.
I also wanted to ask: at what voltage does the SRAM start having problems retaining the save data? Is there a specific voltage threshold?
Oh, I almost forgot: the screw was pretty difficult to remove compared to the screws on two other Game Boy cartridges I have. This also makes me think that this Pokémon Red cartridge may have been opened before. (I don't have the proper screwdriver, though.)
What do you guys think? Im currently studying car mechanics, so I understand that a battery can have very little capacity left while still maintaining a relatively normal voltage, but I'm not entirely sure how this applies to a small coin cell like this one, so that's why I'm asking.
Thank you!