Can the consumer replace the batteries in a Kindle Fire or do you have to have some special knowledge to do it?

Lillian, May have to try hard reset or possibly repair charge port to get battery to start charging. Check the attached links,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
My Kindle won charge
Kindle Wont Start or Charge How to Reset Kindle
Troubleshooting Kindle Fire That Won Charge
Kindle Fire Won Charge Fix

Armend, Could be a bad charging port. Press and hold on button for 15-20 seconds a couple times to see if it will reset and power up before trying anything else. Check the attached links, videos,instruction and guides on kindle charging problems. Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
Kindle Fire Won Charge Fix

12 major Kindle Fire problems and how to fix them

Reset Kindle Fire When it Won Turn on or Charge

Antonia, Check the attached links,about charging problems.
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
12 major Kindle Fire problems and how to fix them

Battery Doesn Charge

Not charging

Kindle Fire Won Charge Fix

Ruby, try pressing and holding on button or you will have to reset.
Check the attached links,
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."

Reset Kindle Fire When it Won Turn on or Charge

My kindle won turn on

My kindle won turn on Is it the battery Kindle Fire HD

Amazon Kindle Won Charge Quick Fixes

Case for Kindle fire HD7,Special Kindle Cover and Ultra Slim Lightweight Smart-shell Cover with Auto Wake Sleep for Amazon Kindle Fire HD 7 4th Generation. Chornic Case for Kindle fire HD7 Special Kindle Cover and Ultra Slim...

sounds like you did everything right
could call amazon see if they can help
or do a factory reset to eliminate software problems you will lose all your data
then there is hardware problems dead battery that won't recharge bad cable connection inside kindle

Reset Kindle Fire When it Won Turn on or Charge

An adapter should have come with your Kindle Fire HD7 when you purchased it. The USB 2.0 cord is universal, so you could plug it into your computer and charge it that way also (while the computer is on).

I am assuming that you checked to make sure you had all the parts. Included in the Box Fire HD 7 tablet, USB 2.0 cable, 5W power adapter, and Quick Start Guide

This is usually a sign of either a failing charger or Kindle, let's try to hard reset the Kindle.
Step 1: Press and hold the power button for 60 seconds
Step 2: Plug the Kindle into the changer, press and hold the power for 30 seconds
Step 3: Let charge for 12 hours
Step 4: Turn on and use the Kindle, if it shuts down before 6 to 8 hours of use, contact Amazon for a replacement.

It is possible that your Kindle Fire's battery has died. If you noticed the battery life diminishing before it wouldn't turn on at all this may be the case. Here is a site that has replacement batteries for the Kindle Fire:
3555A2L Battery for Amazon Kindle Fire D01400

You may need a new power cord or it is possible that your Kindle Fire's battery has died. If you noticed the battery life diminishing before it wouldn't charge this may be the case. Here is a site that has replacement batteries for the Kindle Fire:
3555A2L Battery for Amazon Kindle Fire D01400