I have the Nokia 7+ since March 31. I must say that the battery last a long time: in the morning 100%, the next day around noon 30% (and Nokia gives indication that i still have 5hrs to go) and I use Whatsapp, Facebook, Instagram, Mail, Internet, Google Assistant during that period.
I have the habit to charge my phones when i reach 40% of battery capacity.
I've had my phone since 13th April. I've spent the weekend continually playing with it and Monday being the first day I used it like I would normally. I'm not a heavy user but charged at midnight, and woke up at 6am with the battery at 97%. Took a few photos in the morning before work. I used whatsapp throughout the day, I'm not a chronic messaging but I do send messages regularly. I looked on Instagram maybe 3 times for a few minutes throughout the day. Used the internet briefly once or twice. Changed settings and turned some apps off in background. Streamed podcast for about 2 hours and it was about 75% battery at 7pm.
I looked on Instagram twice, sent a few whatsapp messages. Went to sleep around 10:30 and put it on Aeroplane mode (I usually don't do this). Woke up about an hour ago, turned wifi on, not data, played with some app battery settings, force stopped some apps. It's now 4:30 am and the batter is at 65%. I'd say battery life is pretty solid. If you're a heavy user, the 2 day promise is optimistic or unrealistic. If you're a light user like me, 2 days easy.