Bro I assume you must be knowing that battery does wear out over a time. Given you are using J7 16, must be more than years old and still last 20hrs is pretty cool.
well its not about how old ur device is ok ...its depends on how much apps working or running while u screen is off...and i think lock screen story which we got with the last update is the most useless feature it consumes power so 1st turn it off and check your data cable may b have the problem with ur data cable ......and buy high speed data cable 2.4...
