When you get below 5% you'll notice extreme braking. The battery is dying and trying to tell you to get off before the gyro fails. The first time this happened to me, I remember thinking "what the hell is going on, there's no way I've ridden this thing to zero!" - sure enough, it was red & dead in the app. A full charge and more careful battery monitoring prevented that from happening again.
Your situation sounds like an overnight charge might help recalibrate the battery?