New Dell E6420 Battery is not being recognized

The battery on my Dell E6420 has lost its ability to maintain a good charge, so I decided to replace it after years of use. I now have a genuine new Dell battery. I attempted to install it but the battery is not being recognized by my system. The battery indicator on my laptop is flashing nonstop orange and my PC does not "detect" a battery. My AC adapter is fine and is in good working order. My old battery is type M5Y0X and the new battery is type T54FJ. I have researched this issue extensively and have done the following with no success (listed in no particular order):

-Updated my BIOS to the latest release.

-In the BIOS settings, I tried changing from Express Charge to Standard Charge

-I've shut down my PC, removed the battery and AC adapter, held down the power button for at least 20 seconds to discharge before reinstalling the battery.

-Using Device Manager, I've uninstalled 3 listed entries of "Microsoft ACPI-Compliant Control Method Battery" underneath the "Batteries" tree, and then "Scanned for hardware changes" which then repopulates these three entries.

-Cleaned both connecting ports on my PC and new battery.

I have scoured this community and other online sources and have found no other solutions.