I think besides battery size, the premier factor with batteries is app management. If you have a big battery but some rogue or poorly developed app running it won't matter the size. Conversely, if your phone is lean and running without the battery hogging apps you're good to go.
Here's a good case in point, I had a LG G4 that for the first 8 months was an absolute monster. I run my business from my phone during the day and I'm always on the phone, texting, emails, internet, some apps., many times in areas with bad coverage. Every night I'd go to bed with 35% left averaging 3-4 hours screen time, 1 1/2+ hours on the phone...never even close to running out of battery.
Then MM happened and screwed up something so bad on the phone it would crash at 4:30 every day, sometimes earlier. I gave up messing around with the thing trying to get it to operate correctly and picked up a new S7. Back to great battery life now (much nicer phone also).