You had 2 weeks of "standby time" battery life, but in practice it was more like 3-4 days. I agree all OEMs should be pushing for 48+ hours of battery life, though, at the cost of performance or even higher resolutions and whatnot. Because when they'll promise 2 days of battery life, heavy users will still get only like 1, because with the phones promising 24h of battery life now, heavy users get like half of that. It would be great if everyone could get at least 24h of battery life, which means the "average" battery life should be 48h or more.
3100 mAh shall actually be around 2 days of semi-heavy use. Owning Nexus 4 and 5, they both exceed two days of normal use or 1 day of heavy use, but the advertised oneplus one is going to have extraordinarly larger battery.
So I would say, expect it last two full days as long as you are not overly heavy mobile user.
Yes, not two weeks, but dumbphones never lasted two weeks back these days. Honestly the new smartphones are finally catching up with reasonable battery life expectations than two years ago.
Stock apps, disabled Google+ (it was causing CPU usage spikes on both phoens randomly), minimal/no services running in the background.
My daily usage usually consits of (accumulated): 30min browsing, 1h hangouts, 2h podcasts/music (though pre-downloaded by wifi), 1 minute calls (yes I sometimes use it for calling).
Let me say that 2 days is when I am gentle with the phone, otherwise it is around 1.5. In any case, a huge difference to how were the first smartphones hardly surviving until the evening.