Monitor II ANC Battery Issues

So I've had my Monitor II for a few years so this might just be age but I wanted to check here first. Since a week ago, the battery life has suddenly been incredibly short, maybe 3 hours if I'm lucky. This was not a gradual decline in battery life but a sudden drop off. But that's not all.

So the indicator light does red yellow and green depending on how full the battery is while charging. So my phone notifies me that it has 10% battery left, so I turn it off, start charging it and the light is green immediately. Turn it back on again and my phone tells me "100% battery".

Another instance 3 days ago had me charge it for 2 hours until the light was green. I disconnected it and out of curiosity reconnected it and the light was red now. Do you see what I mean? It's not just the battery, there is some weird stuff going on with it. I also managed to charge it for maybe 10 minutes once and it went from 0% back to 90%. This is annoying because it's so inconsistent and I don't know what to do about it. Look for a potential battery replacement? Reset the headphones? Are the headphones just dead? I would just reset them, but I wanted to check anyways, since I'm not the greatest tech person so maybe someone here knows more about the cause of this.

TLDR: battery life and and charge indicator is very short and incredibly inconsistent. What could be the cause and what should I do?