In mobaliti like phones or laptop poeples wants longer life minimum 1 day of full use of systens like human.
Thats the reason why asus making large battery phones. The backup of battery is not depends in its capacity( mAh) it is depend on build quality.
For example dell battery life is longer than lenovo laptops battery when they have same cells battery.
Same procedure is act on mobile phones.
My freind uses asus zenefone 5 in this 1 year
This phone is dual cote and 2 gb of ram and 2100mAh battery but my xolo battery kife is batter than this phines battery.