>>50232445Gen 1 and Stadium games are probably fine, they don't have a clock chip inside them constantly draining battery so they can last 50 years like NES games. But gen 2 and 3 game batteries die much sooner thanks to the RTC. Gen 3 saves will be fine though even if the battery dies or you change it, they save to flash memory and the battery is only used to power the clock.
Unfortunately there's no way to recover your Gen 1 or 2 save if the battery is dead or removed.