Your battery sounds like it has reached it's end of life.... They do "wear out" over time.
The good news is you can find replacement batteries online, just make sure they match yours exactly, and are Lenovo verified before you purchase.
I like to use Newegg, Amazon and AliExpress for most of my computer parts... just my personal choices.
I do not work for Lenovo, I only provide suggestions based on my personal willingness to help others. All advice and comments are based on my experience, and do not reflect Lenovo policy, terms or conditions.