Laptop won't turn on or charge

Hi,

I last used my personal macbook about 3 weeks ago, during which time it'd boot fine but had battery retention issues. Its charge capacity had severely depleted and with the clip on the bottom of the case popping out, I assumed the battery had swelled and ordered another - Before fitting this battery I tried booting the laptop, but it wouldn't come on, not even a charging screen when plugged in.

I replaced the battery and now intermittently a charging screen will appear for approx 10seconds before disappearing again. This is only when plugged in. When unplugged, its completely unresponsive and won't power up anything at all when pressing the power on button.

From some DIY ventures I have a current pen, which beeps and flashes red when it detects a current flowing - I tested the mac when plugged in and it'll intermittent have a current flowing across the logic board and around the metal casing before stopping completely.

This current transmits for longer times when the lid is shut, and will become more intermittent when the lid is open and it attempts to provide the charging screen.

The current/voltage pen won't even detect a current in the usb-c socket being used to charge when unable to detect a current elsewhere.

At this point, I think the usb-c ports may have shorted resulting in the intermittent charging, but I'm by no means an expert, nor widely experienced in this. I was hoping with the above information, someone more knowledgeable than myself would be able to provide some insight into what they believe may be the issue, or perhaps some troubleshooting measures.

I have a usb-c current meter coming tomorrow, but I suspect this is only going to show me what I already know. At times, it charges for very short times and the rest of the time there's nothing flowing into the laptop.

Thanks in advance,

Adam.