Look, all these great tips for saving your iPhone battery are not very useful if they don’t apply to you. Your iPhone use is uniquely your own, and you really ought to get a handle on how your battery is affected as you apply the various strategies to help conserve power when you need it.
Otherwise, why bother, right? Here’s how to check your battery usage stats right on your iPhone, as recommended by Apple.
Tap into your Settings app, and then tap the General button. Next, tap the Usage area, and scroll down to the area titled, Battery Usage. Toggle the Battery Percentage to ON, if that helps you keep track of how full it is. The battery icon at the top of your iPHone display show a percentage, rather than just a picture.
Note the section called Time since last full charge. Usage denotes the time your iPhone has been awake and in use since you last topped off the battery. Awake means when your iPhone is doing things like making a call, using email, listening to music, or engaged other background tasks like auto-checking email.
Standby is the amount of time your iPhone has been powered on since the last full charge, even if its asleep.
Keep an eye on these two numbers as you adjust your iPhone’s features, and see if they go up or down, or just stay the same. If they get larger after an adjustment, you know you’re saving battery. If they stay the same, you know your adjustment has little to no effect, based on your own actual use of the iPhone. If they go down, go ahead and change it back to the way it was.
Source: Apple Support