I found that this command will generate an HTML file that will let you know the health of a battery:
for Windows 7:
for Windows 8 and 10:
Both need to be run in an elevated command prompt.
You'll get an HTML report that may or may not be able to be opened from where it is stored. When you open the file, if you scroll to near the bottom, you'll see an area labeled "Battery:Battery Information." Here's what my "Battery:Battery Information" looks like on my 10 month old laptop:
Battery ID 1153SanyoDELL YDN874C
Serial Number 1153
Long Term 1
Design Capacity 52592
Last Full Charge 51520
In this case, I see that the capacity of the battery is 52592, but its last *full* charge was only 51520. So if I divide 51520 by 52592, I get 97.962% - so my battery is nearly 98% healthy. This means my battery is in great health, whereas most older batteries will be much lower.
Credit for this information goes to these two locations: