Most likely a drain caused by an app. Look in the Battery details screen for the largest battery use app. If it is anything other than Screen, such as the Kernel or OS, you might consider cleaning the Cache partition in Storage. If that doesn't work, then you might think about a factory reset. If it is anything other than the above, start with your most recently installed app, or clean out the apps you don't need, then perform a Cache clear in Storage, in Settings.
