Quick Symptoms of faulty Battery
if you your battery is not last long draining too quick or charging too quick and battery percentage changes from i.e. 80% to 30% and charging from 0% to 30 in few second or your phone restarts itself or flash logo only this means you may need to replace your battery.
Don’t waste your time with App Store apps
First things first, you shouldn’t waste any time searching and testing third-party apps from the App Store that claim to give you battery information. Since the release of iOS 10, Apple has cut off access to battery details for third-party apps in the App Store, making these apps completely useless.