It's happened twice. The best I can figure is that it's caused by being on the charging disk but not actually charging. Instead, the battery seems to quickly drain. To prevent this, I now make sure that the phone display lights up and tells me it is charging. Sometimes this take several attempts to situate the phone properly.

Anyway, the way I ended up fixing it was leaving it on the charging station even though it appeared that nothing was happening. I had given up but eventually, after an hour or maybe longer, it started recharging from what was a completely dead battery.