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As well as the Guardian article, please also link to the NTSB press release,
https://www.ntsb.gov/news/press-releases/Pages/nr20180607.aspx [ntsb.gov]
The press release includes a link to the full preliminary report, for anyone inclined to read the long version.
...
The Mountain View Fire Department applied about 200 gallons of water and foam to extinguish the post-crash fire. The battery reignited five days after the crash in an impound lot and was extinguished by the San Mateo Fire Department.