Look to the right of the warning...a dark blue circle on a black background (difficult to see in bright sunlight)...poorly designed by the app people. Tap the circle which then becomes a checkmark. Tap the Yes. Sometimes there are two circles that need to be tapped.
Yes, I got this one from Amazon and use it religiously. I have four of the original batteries with the smaller nubs so I stand a greater chance of having one pop out in flight...like some people have.
That percentage you can adjust is the low battery warning...not when RTH initiates automatically. And remember, the auto RTH for battery is based on NO WIND, climbing to RTH altitude, and returning to descend and land.