I just replaced my S6 with S10 and notice a big improvement in battery. My S6 was well used. I would run or cycle for 1hr+ 6-7 times a week listening, tracking distance and speed with GPS + listening to music on airpods. For a 1hr run, it would lose about 35% battery. When I replaced it last week battery health was 78%. I also recently started wearing it for sleep tracking and it would deplete around 25-30% on 7hrs average sleep. I found I was charging it more, but the S6 doesn't have fast charging, so after charging it whilst showing, for example, it might only be at 75% charged and I needed to take it off the charger to use it for the day. Then it would warn me before bedtime to charge, so I would give it a little boost in order to wear it overnight.
The S10? It depletes around 10% overnight. Uses around 20% battery for an hour long run (GPS tracked) + music to airpods. I expect this efficiency is both the benefit of the fresher battery and the S10 chip.