Same
Same experience here on iOS 7, and I've also had much the same problem with iOS 6.
If my phone is around 20% plus or minus a few points, it seems anything can trigger a shut down. It's definitely happened more than once when taking a picture.
A friend told me with his previous iphone he was having similar issues, and he thought that meant it was basically the end of the battery's life...
I'm wondering if most people experiencing this are on older phones. I'm using a 4s that I got when they launched... so i guess it's close to 2 yrs old.
still... seems like software should be able to account for real battery life and adjust accordingly.