Let me start stating every Anker was tested good.
The thing is this, I'm one of those geeks that wastes days reading reviews which powerbank has the least conversion losses.
Say I find that PowerCore XYZ has 93% conversion efficiency it would be great.
Then I receive a slightly older revision of PowerCore XYZ has 'only' a conversion efficiency of 90% that's still good because the worst brands hardly do 50%.
But still I feel Anker 'stole' 3% from me.
Numbers aren't actual numbers. Just a way of explanation