Too late but you should lave looked at (and made a screenshot of) the battery info page. That would have shown the battery temp, voltage, individual cell voltages, and explained whether the battery has an issue (dead cell), temp was too low, or if the alarm was just a fluke. Hard to know now (until we finally get a tool to read the detailed flight logs, hint hint).
ALWAYS look at the info you've got when something's strange.