Why does the laptop battery not charge?

A few weeks back the battery on my MacBook Pro 15” (early 2013, macOS Catalina 10.15.4) stopped charging. The indicator on the MagSafe did not turn on, neither did the System Report show the battery being charged. As my battery was in poor condition I ordered a replacement from iFixit. I also ordered MagSafe board, just in case. Until the new components arrived I could run the laptop fine by disconnecting the battery from the motherboard. The indicator on MagSafe lit up as it was supposed to. But the CPU was throttled down as expected.

After receiving the new battery and Magsafe board, I proceeded with the repair and everything went well. Now the laptop runs on the new battery. However it still does not charge. The Magsafe indicator does not light up as long as the battery is connected to the motherboard. It only lights up when the battery is disconnected.

SMC reset does not resolve the issue, and I cannot run the diagnostics test on this laptop.

What could be the issue and how could it be fixed? Any help is appreciated.