I find my 3DS XL battery is far worse than my 3DS, which is odd seeing as the life is meant to be better. I put it into sleep mode whilst I'm at work for 4 hours, maybe play the Mii dungeon and puzzle games and then turn it off before i get home. Then I bring it in the next day for another 4 or 6 hours (in sleep mode) and by the time i go to check it it's dead. I used my 3DS to do this before I upgraded to 3DS XL and it was fine, it lasted a good few days and didn't die on me in sleep mode. I would walk around cities with my old 3DS all day and it'd be fine. I was just wondering how long everyone else's lasts in sleep mode? Does yours die out in sleep mode pretty fast? Maybe there's a fault with mine. Also, do ROM cards run the battery down faster?