tl;dr version - My AW5 _almost_ lasted through a typical day but not quite...
So yesterday was a fairly typical usage day for me. I follow this pattern 3-4 days a week:
Wake @ 5:45am. Phone usually with me, sometimes leave it at my desk when grabbing coffee or something. 45 minute outdoor run streaming a podcast to headphones, so GPS+cell+BT all on. Typical interactions with the watch setting reminders via siri, checking meetings, acknowledging texts, etc. I did go to bed a little later at 11:20 rather than the more usual 11pm.
AW5 hit low power warning at 9:38pm. Watch at 5% power at 10:53pm showing Usage of 4h 44m, Standby 15h 42min. At 11:20pm I noticed the watch had completely shut down and was unresponsive.
My S4 and previous watches all handled the above without a thought, put on the charger at bedtime, take it off when I get up. I've never needed to worry about the battery unless I'd gone for a 2 hour long run or something where I knew I'd used cell+GPS a lot.
For the curious - AOD on, noise app off, otherwise a normal setup with background app refresh on for most stuff.