The Boeing 787 was grounded worldwide in January of 2013 due to batteries overheating and melting down. On multiple occurrences, the lithium ion batteries, located near the forward and aft electronics bays, overheated and caused the battery to start smoking and burning up.
Since the aircraft grounding order was lifted by the FAA in April 2013, there have still been a couple of battery issues, but none have been as severe as the ones prior to the grounding. The issues that have occurred since the fix was implemented involved Japan Airlines, and before the United issue, Qatar Airways in October of 2014.
On November 13th, United flight 915 was nearing the end of its trans-Atlantic flight from Washington Dulles to Paris-Charles De Gaulle. While on approach, the pilots received a overheating warning from one of the batteries.
After arrival, the battery was found to be dripping fluid through the pipes that Boeing implemented as part of the 2013 fix, suggesting another thermal runaway occurred. A thermal runaway is when an object gets overheated and starts breaking down. The thermal runaway was contained, and no fire started as a result.
The containment of the battery overheating indicates that Boeing’s fix was successful in preventing a serious issue. Boeing did not entirely fix the battery as it still overheated, the system implemented around it was a success. Boeing made minor changes to the inside of the battery, including wrapping the cells in isolation tape as well as giving the terminals locking fasteners. Outside of the battery is where the majority of the changes took place as can be seen below.
As evident from the battery overheating, it is clear that there is still an issue with the battery itself that needs to be addressed. Boeing chose to use lithium ion batteries due to their light weight as they provide a higher amount of power per weight than traditional airliner batteries which are nickel based.
Featured photo from author, battery photo from NTSB