Background refresh will use more battery life because the applications can wake and access the internet to update their information.
Applications can still work in the background for a period of time performing processes before they are supposed to be suspended; believe it is one minute.
Dependent on how many times you open and close the app during the day...
You can open the app one hundred times and it has a total of ten minutes of screen time, but one hundred minutes of background time - if that makes sense.