Maybe I can't be trusted with the answer? As I recall, as your battery runs out, first you can still see % power left but no range estimate. Then you can't get a % either (maybe at < 10%?) That only happened once and I was 5kmish from home, it was summer, and I made it back fine. So how panicked should I have been? Is there a "turtle mode" that kicks in when things get REALLY low? If so, what does it do? And can running the battery that low harm it or does the battery management software take care of that?