A raging fire at the 300MW Tesla Megapack battery storage site in Australia is finally under control.

One of the 13-ton lithium-ion battery shipping containers at the 300MW site caught fire on Friday, eventually flaming out on Monday.

"The Moorabool incident was declared under control at 3.05pm on Monday 2 August," Victoria's Country Fire Authority said in a statement.

"Firefighters have successfully completed the operation of opening all doors to the container of the battery, with no sign of fire."

A smaller number of firefighters and fire trucks from CFA are remaining on scene through the 4th as a precaution and will take regular thermal temperature readings to monitor damaged units.

It is not yet known what caused the fire at one of the 210 Megapacks at the site, run by operator Neoen Australia. Two other battery packs were also damaged by the fire, but did not themselves join the blaze.

The battery storage site was being tested and was not connected to the grid.