mobile

My old phone's (Xperia S) battery drains very fast (can't last for a day) after 2 years of use. When it was new it lasted about one and a half day. I charged it every day for 2 years and the battery became weaker. I don't want this to happen with my Z2. I use dock for charging my Z2. USB cable or dock is better for the battery? And when should I charge it? wait while the battery drains full or charge it every day and don't let it drain, just about half, or don't charge it full and get it drained every day. And how long should I charge it? just that time while it charge full or leave it charging for longer (a whole night, about 10h)