Re: How long does the save card last?
From what I can find by googling, DS games don't have an internal battery like Gameboy and Gameboy Advance games. They get their time from the DS itself and the save files are saved to a flash drive thing like in SD cards. So it should have a life similar to an SD card, which is apparently 10+ years.
There are also apparently ways to back up the save files if you're worried!