I am new to the iPhone world. The battery life on my 4s seems to be good - no complaints. I want to keep it that way. By the end of the day my battery is usually down to between 10 and 20%. I charge it over night. Should I be charging it at some point during the day to prevent it from dropping below 20% on a daily basis? Or as long as I'm not letting it die completely regularly is below 20% okay? I have been researching but haven't found the best answer - it seems different people have different theories on this?