This is where the preparer actually earns what they charge. Per the instructions:

Line 4b
Enter 100% unless the vehicle was a vehicle with at least four wheels manufactured by Tesla or General Motors (Chevrolet Bolt EV, etc.).
Tesla. Enter the following percentage if the vehicle was
manufactured by Tesla.
• 100% if you purchased it before January 1, 2019.
• 50% if you purchased it after December 31, 2018, but
before July 1, 2019.
• 25% if you purchased it after June 30, 2019, but before
January 1, 2020.
The credit is not available for Tesla vehicles purchased
after December 31, 2019.

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We need to enter the Phase-out Percentage in the line right below where we enter the KWH