8-10 hours, if you're using it, isn't bad. 8-10 hours if it's just sitting there with the screen off is pretty bad.
Install
Greenify and Greenify any apps you don't want running unless you run them (phone, text, email should run when they want, or you won't get anything incoming until you run the app).
Fully charge the phone, let it sit all night, then look at the battery stats (where you saw Android System and Android OS battery use) and tap the graph at the top. You'll get a second page. Look at the Awake line at the bottom. It should be dark except for a few thin lines, except when the screen is on. If it's not, something is keeping it from sleeping. You can use
Wakelock Detector to determine which apps are doing that. (See
Wakelock detector with non-rooted phone if the phone isn't rooted. It's a pain, but you won't be doing it more than 2 or 3 times.) Either Greenify the apps doing it or disable them.
