Replace 2015 MacBook Pro Battery?

My MacBook Pro (Retina, 13-inch, Early 2015), still under 3 year extended warranty, started losing charge quickly. The Recharge Cycle Count is "279," Condition "normal." It goes from 30% charge to 0% overnight while closed. I find myself plugging while I use it to avoid finding it dead the next morning.

Two questions. (1) Do I need to replace the battery or is there some other battery draining problem? (2) Will my warranty cover the battery replacement cost?