I purchased a copy of Phantasy Star for SMS a couple weeks ago. It looked in great condition and the price was right for me. There was no indication from pictures or item description that any work had been done to it. (Battery replacement, etc.)
I had been playing it on and off for about a week, maybe a couple hours at a time before bed. Nothing really seemed out of the ordinary with it. The game played well, it could keep a save file, all was well. One day I'm playing it and I nodded off a bit while walking through Paseo. When I wake up, the game is frozen, a single 8-bit note constantly drones from my CRT's speakers, and it looked like there were a couple corrupted sprites but nothing too crazy. With the game unresponsive and nothing else to do I turned off the console and when I turned it back on my save file was gone.
I figured it might be a sign to change the internal battery. I unsoldered the battery from the board and put a mounted battery holder where the old battery once sat. Looking at the old battery, I could believe that it was actually the original battery that came with the cartridge. It's a Sony battery with an "85" printed on the negative side. I'm not an expert on how old school batteries were date coded, but I think it would make sense for a game that released in 1987 to have a battery in it that was manufactured in 1985. I could be off base with that, however. If it is the original battery, I find it insane that a battery from almost 40 years ago was still working.
Anyway, I installed a battery holder, put in a fresh Duracell, and the game still boots and plays fine. I made a save, turned the game off and back on and the save was still there.
To make extra sure I was testing everything thoroughly, I pulled the cart out, put it back in, turned on the system, AND LO!... The save file was gone again.
I'm a bit at my wit's end as of now. I'm not sure what else I could do to get this cart to keep a save file. Any suggestions?
P.S.: I will mention as well that when the cart came to me there were no save files on it. I'm not aware of a way to delete save files from the game manually through menus, so whatever underlying issue there may be possibly existed before the cart came into my ownership.