1. How long have you've had the phone ?
2. Case To Case Basis ... how you charge it.
3. Yes it's Lithium Ion Battery and usually in this case you can charge it anytime low bat full bat.
However, sometimes when you are charging from Point of Connection to the Charging Circuitry to the Battery. Could be a Flex issue or connection issue inside that's if it's a built in battery. However in this case
seems like the battery has taken it's toll or you just got a lemon. Usually Lithium Ion batteries last 3 years. I have a Lithium Ion battery that lasted me from 2010 - 2017 and it's still charging and working. So
depends on how it's charged. I don't know the history of your charging cycle . Best to give more detailed information. When it was working to the point when it stopped working. Thanks
Answer: Replace Battery to isolate the issue.