You could buy 100 iphones... Or you could "borrow" a million for free, to get rock solid stats.
Also there are hundreds, if not thousands, of different phone models. The allegedly used way of negative testing is much better than buying phones, and is virtually free.
"Borrowing" a million phones and draining their battery down would make increase the perception of your app draining batteries.
Seems pretty dubious if you would be willing to do that just to get a bit better low battery prices.
Coming from a business whom founder said: "I have over 4,000 emails, pictures, addresses, SMS... People just submitted it. I don't know why. They trust me. Dumb f**s", ethical considerations has zero weight here.
Also there are hundreds, if not thousands, of different phone models. The allegedly used way of negative testing is much better than buying phones, and is virtually free.