The failure struck at 0830 on Saturday morning when the car was first switched on after the KERS battery had been charged overnight.
The team will conduct a full investigation into the cause, but when asked if Williams had experienced any similar failures, chief race engineer Xevi Pujolar replied: "No. [It happened] when they switched the car on at 0830 in the morning to get ready for the warming up, that's when it went wrong.
"We are still investigating what went wrong within the battery pack."
The KERS failure did not cause any further damage to the car, with Maldonado able to run in both free practice and qualifying, earning 18th place on the grid.
"There was no damage because it was in the battery pack," said Pujolar.
"You remove that bit and it is fine and the car was OK."