Sometimes my Kindle Fire HD can take up to 19 hours to get to 100% using the superfast charger, I have tried the usual reset, ran the battery down to under 15% and charging overnight, when I get up in morning after it being on charge for 8 hours it maybe sitting at 40 - 50%. Had my KF for 7 months and use it daily, well try too. Anyone had similar problems, interesting to find out.