The LG V20 has a 3,200 mAh battery that can easily get you through the day without any trouble. But if you are more extreme and power user probably even this wouldn't be enough. And instead of buying a secondary battery, why don't you actually consider the ZeroLemon option. The case company released on Amazon their case at just $60. It comes with a 10,000mAh battery that goes in the same slot where the usual one goes. The removable back metal panel of V20 is substituted by the rubber bumper case that goes around the whole device plus, of course, the enormous...
Source: http://www.gsmarena.com/this_battery_case_will_give_your_lg_v20_more_than_5_days_life-news-22885.php