When you say S9, I assume you mean a samsung galaxy? Because that's exactly my previous phone, purchased in 2018 and now the battery health is poor, the usb barely works, the power button is entirely missing and well.

With my previous battery time I'd say it survived maybe 4-5 hours of youtube.

Meanwhile I've now been in bed with my Xperia 5 IV and after say an hour check my battery which I'm used to dropping by like 20-25% having only dropped like 4. (I'm generalizing, but it really felt that way)

Either way I got very used to charging my S9 every day, sometimes twice a day.

Meanwhile I've only charged the 5 IV 3 times so far and I got it like 8 days ago.