Since Android 10 updated battery performance of my Zenfone 5z has become unreliable. On few occasions battery lasts for 6 hrs of screen on time but sometimes it lasts for only 3 hours of screen on time. Both observations are made after Charing the battery to 100% and operating under very similar conditions.
Data on only when using the phone, Wifi on only when using the phone, low display brightness, bluetooth always off, location always off, NFC always off.
I found that restating the phone after fully charging it tends to give close to 5:30+ hrs of screen on time as opposed to 3hrs when not restarted. But this doesn't always work.
Android Pie and Oreo never had this problem, I was getting consistent 6+ hours of screen on time.