Slow charging issues on my MacBook Air

My Mac book air retina 2020 won’t charge at night and even when it does very little, I can’t charge while at school even if I plug it in a leave it. I’ve purchased a battery pack as when I plug it in it doesn’t die but also won’t charge. There was one occasion where it did start charging very slowly in school. I’m looking at getting the battery replaced but I get the feeling it’s not the battery but possibly the power adapter in the device or something else. Can someone help?

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