I put 50 or so hours into Sapphire before giving up on it cus the internal clock battery died and i thought that mirage island (which the battery is needed for, i believe) was the location of the final gym and I couldnt complete the game. Whether that's actually true, idk, but I was 12 and didn't think to look it up (this was a time when my understanding of the net was very limited) so I just never beat that game lol.
Yellow, I was at the indigo plateau, just beat Gary i believe, when my save battery died. WAs at the final stages (?) of the TCG video game when the same thing happened.
I was fairly far into FireRed, almost at the end i think, when someone stole it, along with my gameboy and favorite cards.
There was also a time as a young kid when my brother and I got into a fight and he did something to the PS3 (aggressively mashing the power button or something, I don't remember) that caused a hard reset of some sort, and deleted every Minecraft world we had