The battery powering the underwater locator beacon on missing Malaysia Airlines flight MH370’s data recorder expired in 2012, a report has found, but no red flags were raised relating to the crew or aircraft.

Apart from that anomaly, the detailed report released on Sunday devotes page after page to describe the complete normality of the flight, shedding little light on aviation’s biggest mystery.

The significance of the expired battery was not immediately apparent, except indicating that searchers would have had lesser chance of locating the aircraft in the Indian Ocean, where it is believed to have crashed, even if they were in its vicinity.

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The report says civilian radar had tracked the plane for a short time after it diverted on March 8 of last year, apparently contradicting earlier Malaysian statements that only its military radar had monitored the plane.

The Fugro Discovery is part of a the search for MH370. Photo: AAP

The two instruments are critical in any crash because they record cockpit conversation and flight data, leading up to the end of the flight.

The 584-page report by an independent investigation group also goes into minute details of the crew’s lives, including their medical and financial records and their training, and mentions no findings that cast suspicion on them.

“There were no behavioural signs of social isolation, change in habits or interest, self-neglect, drug or alcohol abuse of the captain, first officer and the cabin crew,” it says.

The report also details the aircraft’s service record as well as its maintenance schedule, weather, communications systems and other aspects that show nothing unusual except for the one previously undisclosed fact of the battery’s expiry date.

It says that according to maintenance records, the battery on the beacon attached to the flight data recorder expired in December 2012.

“There is some extra margin in the design to account for battery life variability and ensure that the unit will meet the minimum requirement,” it says.

Relative of a passenger on the flight protests to keep the search going. Photo: AAP

“However, once beyond the expiry date, the (battery’s) effectiveness decreases so it may operate, for a reduced time period until it finally discharges.”

While it is possible the battery will operate past the expiry date, “it is not guaranteed that it will work or that it would meet the 30-day minimum requirement”.

Pilots’ movements watched on CCTV

Investigators behind the report studied the pilots on CCTV recordings on the day of the flight and on three previous flights and observed no significant behavioural changes.

The report also found the aircraft was airworthy at the time it went missing.

The report ticked through a number of the plane’s mechanical systems and noted in each case that according to available data and maintenance records, nothing alarming was seen.

Suspicion had fallen on the cockpit crew of pilot Zaharie Ahmad Shah and his co-pilot Fariq Abdul Hamid, with other theories including a mechanical problem or hijack.

The report was focused on air safety issues related to MH370, and the investigators did not probe the 227 passengers or the possibility of a hijack.

It stressed the investigation was ongoing and that “new information that may become available may alter this information”.

“The investigation team expects that further factual information will be available from the wreckage and flight recorders if the aircraft is found,” the report said.