Firefighters in California had to put out the smoldering flames coming from a Tesla Model X battery involved in a March fatal crash, even days after the crash, .

KTVU said Thursday that it had obtained a 13-page safety alert penned by the fire chief of Mountain View, California, where the crash took place. The chief, Juan Diaz, highlighted the issues firefighters faced when responding to the March 23 crash, which left the driver, 38-year-old Walter Huang, dead.

The main issue, the report says, is the battery is still charged even after the crash. Here’s more from :

Firefighters say they put the fire out in two minutes but soon discovered the battery fire in the electric vehicle would smolder for hours and reignite multiple times, even days later.

“The battery began to overheat even though we had already cooled the battery and it continued to reignite,” said Diaz. “We don’t have the tools to deal with a battery that is completely, basically destroyed.”

The problem, he says, was a lithium-ion battery that continued to flow with electricity after it was damaged in the high-speed crash, which the NTSB is still investigating.

Tesla engineers had to be called to help dismantle the battery, the report says, but issues persisted.

In the Tesla crash, firefighters called Tesla engineers who had the tools and training to partially dismantle the battery. But even then, the threat wasn’t over.

“In this particular case, six days later, the temperature inside those cells increased to the point of ignition. That’s why the car reignited,” said Diaz. “You have stored energy that is frankly unstable.”

Tesla, for its part, offers online training for first responders to understand how to combat an electric vehicle battery fire. In a statement from Tesla highlighted by KTVU, the automaker said that when a fire does occur, its battery packs are designed to ensure the fire “spreads slowly so that occupants have plenty of time to get out of the car.”

“According to witnesses, that appears to be what happened here as we understand there were no occupants still in the Model X by the time the fire could have presented a risk,” the statement said.

The National Transportation Safety Board this week involving a Tesla Model S that left two dead. The agency said it’s looking primarily at the emergency response in relation to the electric vehicle fire that was sparked by the crash.