I've been reading around and it seems there are a fair amount of people having issues. Hopefully a fix comes quickly. I'm in the US, so at least in my case the issue is present over here as well, yeah I've only had the phone for about 20 hours so we still fairly new to this, I think today we will see more of these issues come up.
I was told by a genius at the apple store upper west side/NYC that this is a documented issue - for iPhone 5's RESTORED from prior iTunes backups, many phones have had battery issues.
They tested my iphone5 and determined that the battery met or exceeded all specs.
There is a setting: General > Usage > Time Since Last full charge:
-- if the usage and standby times are identical, there is clearly a software issue. This was the case for me.
I was instructed to NOT restore from backup, rather I am to wipe the phone and treat it as new.
Email accounts can be "restored" from iTunes if Mail.app has them. All other settings must come from the cloud, or they will be lost. I will lose my text history and voicemail password.
I will have to tell iTunes what media and apps I want to sync and re-organize my apps. That's a royal PITA.
I'll report back if this solves things.
Genius said many many people have had this issue... but a full wipe and reconfigure from scratch will fix things. I'll report back tonight.