NASA ISS On-Orbit Status 4 February 2015, SpaceRef
"Automated Transfer Vehicle (ATV)-5 Status: Yesterday, ATV experienced a failure with Battery Power Chain #4. ATV ground teams have confirmed the failure is real and not a sensor issue. The ground teams have taken the necessary precautions and are continuing their investigation. The vehicle has a total of four power chains. Should a second power chain failure occur, an expedited undocking would be required within 24 hours per ATV Flight Rules. Break Up Camera (BUC) and Reentry Breakup Recorder (REBR) are currently scheduled to be installed inside ATV next week with a nominal undocking occurring on Saturday, February 14th."
Marc's note: This is not a significant issue at this time from the limited information available. Perhaps the 11:00 am. scheduled Space Station Live update will provide an update.
Marc's update: During today's Space Station Live the issue was mentioned with no new information. At this point everything is on track for the Saturday, February 14th undocking.