How come sometimes when you play old Pokemon games on old devices, you're progress gets erased?

Question

I have seen this happen loads of times, whether it's YouTubers, or just friends. Is this just people deleting files, or is it like a glitch?

Comments

Also, I noticed that you haven't chosen an answer on any of your questions. When you see an answer you like press the check mark by it.

Answer 1

The cartridges have internal battery type things. And when these go out, your progress will be erased.