How long does it take to charge a DSi?

No, ID1664098201 it takes about 1 hour to fully charge possibly 2 if it is on red and flashing (if it dose that you need to put it on charge immediately) if it took 2-4 hours that would be ridiculous and 21 hours?? That is just... No way... It would NEVER take that long no matter HOW LOW the charge is.