My headphones battery is acting strange

Hey, so I have my headphones since I would say five years, but recently they've been acting strange.

Whenever I charge my battery for a long time, it will go down to 10% pretty fast but last for days on 10% battery. I don't know if my battery is really used cause it seems like for some people it's a cable issue, and since I already opened my headphones to repair the left (or right, i don't remember) speaker not working I'm afraid I moved a cable that causes the battery to not work as it should?

Should I try to replace my battery or could it be another problem? Is it even worth it to get a replacement battery on Amazon? I mean for phones I don't really care but for headphones I don't want a bad quality replacement battery to blow up on my head.

Thx for the help!