(from camera test team member Elizabeth Swoope)
The battery indicator in the app causes a lot of confusion. Unfortunately, a lot of people get the idea that it's like the fuel gauge on a vehicle and that you can run the camera until the indicator is empty. That is not the case.
The battery indicator is an indicator of voltage level, not "fullness". Full voltage is 5.7 (or higher), and you'll see P5 on the info strip.
As soon as the batteries drop below 5.7, they'll show 5.1 V, even if they're somewhere between 5.1 and 5.7. You'll see P3 on the info strip and P number and battery indicator may fluctuate between 5.7/P5 and 5.1/P3, with night photos (flash) showing lower and day showing higher.
Maybe we'll see a change in the indicators at some point. In the meantime, I've put together this chart that I hope may help you think differently about what the battery indicator really means.