Any quality phone will / would "under promise and over deliver." What I mean is, you lie about being at zero charge when you really have one or two or three percent left to give the user time to get to a charger. This is better than turning off because it allows time for circumstances that don't allow the user to plug into a charger. Having a bit of breathing room means that one can call emergency services while on the way to plug in, for example, rather than being screwed because it's a ten minute walk home.