That really depends on the settings and usage of the user of the iPhone (5).
We have two iPhone 4S phones and we have an average battery time of 1-1,5 day (when using it for e.g. a few calls, texts, mail, news apps and a short video for e.g. total of 3-4 hours) or even 2 days (if i don't use my phone much almost 90% stand-by time) and with WIFI connecting for about 90-95% of the day and ofcourse phone network but no 3G.
Aside from that we have the following settings:
- bluetooth off
- screen brightness set to approximately 30%
- fetch e-mail accounts once an hour (Settings > E-mail, calendar .. > deselect 'Push' and set it to either Fetch e.g. once an hour)
- do not refresh any apps in the background (Settings > Refresh apps on background)
- apps that use GPS are limited (Settings > Privacy > Location tracking)
- only have a few apps (5-10) that are allowed to send push notifications
- only have a limited amount of apps to send messages to 'Notification center' or e.g badgets/strips/sounds/apps symbol or on your 'Access screen' (See Settings > Message center > check settings per app)
I think that 3G uses more battery then WIFI so if you have WIFI access then use that instead of 3G.