Dell Inspiron 5535, plugged in not charging.

. My Dell Inspiron 5535 is charging only up to 66% and stops.

. I now have Windows 10, upgraded from Win 8.1 over a year ago.  It had been correctly recharging until about a few weeks ago, when it charged to 86%, and then to 68%, and now 66%.

. I have tried:  removing AC cord, re-booting, also removing battery and reseating.  I have uninstalled the Microsoft AC adapter file and the ACPI file, and they reinstalled when i powered on again.  My cords all appear in good condition.

.  computer starts and operates successfullly without the battery.  

.  I tried to update the drivers, but the response was the drivers available are current.

I am "assuming" the battery is bad, but purchasing a new one might not fix this problem.

Any ideas or help please?  Thanks.