The dropoff is sharp but not instant. If you're measuring 2.9V, that's around 5-10%, you should replace that now, if you don't, you might have a few months left. 3.1V pretty much means no worries, check again in a decade. I've only ever once had a SNES game lose its saves due to a dead battery and that was 20 years ago, the battery must've been faulty from the start, now I sometimes lose saves due to bad contacts making the CPU overwrite the saves with garbage. Sometimes I hold an LED to the battery to see if it still shines brightly. Usually it does. Reminds me, I gotta check on the suicide battery of our Turbo Outrun. In 2016, I checked all our local arcade's SEGA Suicide Battery games and replaced them all, but I didn't know Turbo Outrun had one until like 2 years ago, but it was also still well above 3V (the others were at 2.9something or 3.01V). Made in 1988. Btw. Baby me got a "singing mug" roughly around '87. The entire circuit is potted in the bottom of the mug. It still works. (I've only used it like 3 times in the last 2 decades though)
The dropoff is sharp but not instant. If you're measuring 2.9V, that's around 5-10%, you should replace that now, if you don't, you might have a few months left. 3.1V pretty much means no worries, check again in a decade.
I've only ever once had a SNES game lose its saves due to a dead battery and that was 20 years ago, the battery must've been faulty from the start, now I sometimes lose saves due to bad contacts making the CPU overwrite the saves with garbage. Sometimes I hold an LED to the battery to see if it still shines brightly. Usually it does.
Reminds me, I gotta check on the suicide battery of our Turbo Outrun. In 2016, I checked all our local arcade's SEGA Suicide Battery games and replaced them all, but I didn't know Turbo Outrun had one until like 2 years ago, but it was also still well above 3V (the others were at 2.9something or 3.01V). Made in 1988.
Btw. Baby me got a "singing mug" roughly around '87. The entire circuit is potted in the bottom of the mug. It still works. (I've only used it like 3 times in the last 2 decades though)