I was getting about 10-11hrs of usage time and over 60hrs standby time on a single charge. Though I feel like my battery on my 6S Plus 128GB began to drain faster when I performed my first full power-cycle (drained from 100 to 0) about a week ago. I bought my 6S Plus about 3 weeks ago, setup the device as NEW, no restores from backups, no OTA updates (all through iTunes). No animations, no transparency effects, no background app refresh, no location services, no Bluetooth, brightness is manually set and usuall on the darker side, reduce white point is ON, no iCloud activity at all, wifi on only when in use. Lately I've been getting roughly 8.5-9hrs usage and 40-42hrs standby on a single charge.
As I'm writing this post I'm on 62% battery with 3h52mins usage, 28h35mins standby. Is that any good?