Does my battery need to be replaced? Or is something else going on?

My OP-1 hasn’t kept a charge in over year.

However, up until last week it’s always worked when I plugged it in.

Now it won’t turn on at all.

Is this a battery issue or something else?

Also, while I was previously able to use it when plugged in, it would often give off a constant high pitched hum until I unplugged it and plugged it back in…