My old ipad (I think is 3rd gen) is only 10% down, but cannot run ios 11. I use it to run Harmony Hub and leave it in the tv room. My less than one year old ipad pro is 13% down, not too happy with it down so much so fast. My iphone 5s is 24% down, not bad for its age. can still run ios11.
My new iPad Pro is now showing 9% down. Read some where that the battery apps are not accurate.
The fellow at iRepair said the same thing, so, although I wouldn't say that 5% down is better than say 9% down, with my old battery it was over 50% down, so I would use a battery app as a guide or perhaps rough confirmation, but not an accurate representation of battery life.
In the same way that you need a big draw to properly test a car battery, you'd need a larger draw than a battery app can apply, but it can give a rough indication, or perhaps confirmation of what you already see with battery life.