I used to charge my iPhone 6+ at work, but lately I've been letting it go, to see how it does when paired with the watch.
A typical work day looks like this: I get up and put the watch on at about 6am, exercise about 20-30 minutes, receive dozens of notifications, reply to at least 10-20 messages and make 5-10 phone calls (on the watch), use my iPhone to listen to music (wired earphones) about 2+ hours a day, also check and respond to emails (two Exchange accounts and one iCloud, all pushed) all day (50-100 emails) and surf the net quite a bit, if I have time.
At the end of the day (11pm or so), I'm averaging about 20-30% on the watch, and 10-20% on the phone.