During our ride today, my wife's E3 Vibe+ shut down unexpectedly. The battery was showing 3 out of 5 lights but the display would not turn back on. Got it home, charged it fully and the display turned on normally. That has never happened before so I was wondering what might cause that. The battery is not quite two years old, and hasn't been used very much. It was kept at about 80% over the winter.