A coolant leak is likely to blame for a fire at Victoria's $84 million Big Battery, which is set to resume testing this week.
Following an "unlikely sequence of events" in July, one of the Tesla megapack batteries at the site in Moorabool, near Geelong, caught fire during initial testing before spreading to another battery.
It took firefighters four days to bring the blaze under control.
An Energy Safe Victoria investigation has determined the most likely cause of the incident was a leak within the megapack cooling system, which caused coinciding short circuits in two locations that led to a fire in an electronic component.
These occurred while the megapack was off-line in a service mode that removed fault protections.
"Enabled by this unlikely sequence of events the fault was able to go undetected and initiate a fire in the adjacent battery compartment," according to EnergyVictoria.
Firmware modifications and several monitoring measures have been put in place to prevent another fire at the site.
Energy Safe Victoria has cleared French renewable energy giant Neoen, which owns and operates the battery, to resume testing at the site on Wednesday.
"Safety is our first priority. We have taken the time to understand the cause of the incident and we have implemented actions to ensure it will not happen again," Neon Australia's Managing Direction Louis de Sambucy said in a statement.
"We are now actively working with all stakeholders to complete commissioning and testing of the project and we look forward to sharing the lessons learnt with the industry in coming weeks."
The Big Battery is scheduled to begin operating in November, ahead of the summer peak demand period.
Once completed, the project will have a capacity of 300 megawatts and 450 megawatt-hours - more than double the size of billionaire Elon Musk's Tesla big battery built in South Australia in 2017.
It is also a key component of the Victorian government's plan to reach 50 per cent renewable energy by 2030.
