Do you ruin the iphone battery if you charge when its not empty?
If you let it drain every fifth or sixth charge you will be fine. I occasionally use this app called Ilumination to help drain my battery. it's a flashlight app and drains the battery pretty quick.
No that charges it faster
You won't ruin it but it's better to wait until it's depleted or near so. Batteries have memory and if that memory is exercised to its full capacity, it will last longer.
I've heard it's bad to do so and I experience it now with my iPhone. My phone drains about half way and then I charge it which isn't good. Reason I do it cause I always want a full charge displayed