I seem to be having this issue with my s10+ since launch. I can be on 100% at 10am and 88% at 11am when I haven't even used it.
Really hoping Samsung fix this soon.
After posting my problem about the phone switching its screen in the shirt pocket I have found an option that takes care of that...
...Go to definitions - Advanced features - Motions & gestures - Lift to wake (toggle off) - Double tap to wake up (toggle off).
With this you'll see a big improvement.
I have the same problem. Unplugged my S10+ at 6AM with 100% it's now 4:14PM and I'm on 58% with only 56 minutes screen on time. I’m used to having around 75% from previous phones with this usage and the S10+ will be going back if this isn't fixed soon.
Spoke to Samsung Support on the phone earlier.
Apparently the battery takes between one to two weeks to figure out our usage pattern, then the battery kicks into full throttle and we can expect better battery life.
I have a reference number so I'll give it two weeks and see what happens.