Battery life
Why do I only get about 48 hours off of a full battery charge?
Apple Watch SE, watchOS 9
That is pretty good.
The Ultra 1,2 is rated at 36 hours
The Series 1,2,3,4,5,6,7,8,9 and SE models are rated at 18 hours.
Strongly recommend you NOT take the battery to zero, except is very rare situations, as that is the fastest way to destroy a Li-Ion battery.
Apple Watch Battery and Performance - Apple Support