Cartridges from the 8-bit and 16-bit eras of consoles had a battery to maintain the save data. Aside from passwords, this was pretty much the only way to keep your progress. But, like all batteries, they eventually loose power and can no longer retain the memory of the RAM.
Batteries on a chipset can be replaced in some cases, but once the console is turned off, the data would be lost without a viable way to save it internally. Twitter user Wanikun found the option of losing the save data to Umihara Kawase unacceptable and left the Super Famicom powered on for 20 years to do so.
Even after moving, it seems that the Famicom is again plugged in, the save data still intact.