When charging your Kindle Fire HD, use a power adapter vs. connecting your device directly to your computer to speed up the process. You can also either set your Kindle Fire to sleep mode or turn the power off while you're charging your device to make charging more efficient.
Using a Power Adapter
The fastest way to charge your Kindle Fire is to connect your device to a power outlet with a micro-USB cable and a compatible micro-USB power adapter, which helps accelerate the charging process. Charging your device while using an adapter can charge the HD 7-inch in under four hours and the HD 8.9-inch in under five hours, depending on the adapter and device. If you don't use a power adapter, Amazon estimates that connecting your Kindle Fire directly to your computer using a mirco-USB cable will charge the HD 7-inch in approximately 13.5 hours or the HD 8.9-inch in just under 14 hours.