Does iPhone Battery go down when turned off?

I'm going to a concert tomorrow and I was wondering if the battery will stay at 100% if I keep it off for most of the day. I'll be there for 11 hours, with obviously no way to charge… Any help, or tips to keep battery up, part from brightness and Wi-Fi off would be appreciated. Also, I'll me taking pictures and videoing during the show, so can any one guess how long it will last?

Added (1). *be taking pictures,
And obviously, I don't have two spare phones, so USEFUL and accessible tips would be extremely helpful and muchly appreciated

Don't use flash, keep phone on flight mode

I don't think so but turning it off and turning it on will use a bit of battery

How ever it, s a good cellphone with a good stand by time energy saving, with so much work, I think it, s better to take two more spare phones with you! Good juck. So long.

My opinion iPhone. Paying attention to just a few common sense pointers will pay off with a… "Battery life" means the time your iPhone will run before it must be recharged… Go to Settings > Brightness & Wallpaper and set Auto-Brightness to On. Turn off… Per month (charging the battery to 100% and then completely running it down).