Harry Burkhart, 24, was originally charged with 37 counts in connection with 12 fires over New Year, in a spree allegedly triggered by anti-American anger over his mother's fight against extradition to Germany.
On Tuesday the 63 further charges were added, bringing the total to 100 criminal accounts involving 49 fires.
Authorities say Burkhart launched the attacks, which caused millions of dollars in damage but no serious injuries, the night after making a foul-mouthed anti-US tirade at a court hearing for his mother on December 29. Most of the fires affected cars, but some buildings were also damaged.
His mother Dorothee Burkhart is wanted in Germany on 19 counts of fraud, notably for failing to repay security deposits to apartment tenants and defrauding a Frankfurt cosmetic surgeon out of some $10,000 for breast augmentation surgery.
In addition, state prosecutors in the town of Marburg, Hesse, are investigating whether Harry Burkhart is responsible for a fire in the small town of Homberg.
LA prosecutors allege that Burkhart went on a "binge" of arson attacks fired up by anti-American "hatred" fuelled by his mother's fight against deportation to Germany.
"The string of fires terrorized residents of Hollywood and the Westside," said District Attorney Steve Cooley at the time.
Harry Burkhart was reported as appearing confused at his initial hearing at the beginning of January, and his mother has described him as mentally disturbed.