Your V20 isn't that old so while the battery could be failing that isn't likely. If things have been more or less OK and then just recently became a problem, it wouldn't be surprising the source of whatever is going wrong is just a temporary glitch. Try just powering off your phone and then restarting it, this resets everything.
Also, if you look at the Settings >> Battery menu, is there anything that shows up as using a lot more battery power recently?
Your V20 does have a user-replaceable battery so replacing it is a last resort option.