Freaky battery delemma

I’m trying to figure out why my battery will not charge. I have a Dell Inspiron 15R SE 7520. First, I was running Windows 7, and it would only charge to 80%. I recently installed Windows 10, and the problem went away for a while, but it is back. Now the battery seems to be stuck on 64%. I ran a Pre-boot test, and here are the results:

Primary Battery Charge: Current = 64% / High = 64% / Low = 64%

Primary Battery Health: Current = 83% / High = 83% / Low = 83%

Primary Battery Voltage: Current = 12136mV / High = 12138mV / Low = 12136mV

Primary Battery Current Flow: Current = 0mA / High = 0ma / Low = 0ma

Primary Battery Charging State: Current = Idle / High = n/a / Low = n/a

I have a voltmeter and checked the output of the AC adapter, and it was fine (15 volts). I took the battery out and back again, but no good. I bought this new in 2012, and it is the original battery. When I look at the battery icon, it simply reads 64% and the power mode says “plugged in.” Any advice would be greatly appreciated! Thanks in advance for your expertise.