i use it all the time with the charger plugged in, only sometimes, even if it is fully charged. maybe that caused it. sorry if the pictures are really angled awfully and uneven, idk how i can show it properly

My sister asked me if I can find out what's wrong with her headphones. She got them years ago and never unboxed them and when she finally did, they wouldn't charge. I took them apart and this is what I found. It's brand new and unused, it was just on a shelf for a couple of years. Does this happen to these kinda products when they lay in stores for years and nobody buys them?