Dell Laptop Inspiron 5520 battery charging issue

I have had my Dell Inspiron 5520 Laptop since late 2012. It has been a great computer, and although I have recently upgraded to a new Dell laptop, I still use my 5520 for writing and entertainment purposes. The only reason I upgraded at all was because I had a hard drive go bad and didn't realize that it was only the hard drive at the time. I restored the computer with a different version of Windows 7 after I replaced the drive and everything is working great - except the battery charging. It is sporadic. What happens is I plug in the charging cord at times, the computer detects it for a second or two, and then it no longer charges. I ran a complete PC health check and it showed everything is working properly and the battery is healthy, but it did not detect it being plugged in even when it was. I also flashed the BIOS, and it had no real affect on the charging issue. WHAT DID WORK was shutting down the computer, removing the battery, and pressing the power button for 30 seconds and reinstalling the battery. After I do that, it does detect the charging cord is connected and the battery charges properly - but only for a week or two, and then I usually have to do it all over again. Any thoughts? Is my battery going? Charging cord? Any other thoughts? It's not a HUGE deal that this is happening. I love this computer. If I can correct the problem, I will. Thanks!

PS - The original dell software had a feature that I could set that ran the battery up and down even while plugged in to preserve battery life. After I reinstalled everything available from the Dell website, this feature was no longer detected on the computer. Just wanted to put that out there so all the information I have is offered.