It is in the LEAF Warranty Information Booklet. In the 2018 booklet, I find the following text (bolding after heading is mine):
2018 LEAF Warranty Information Booklet, page 9 wrote:MAINTENANCE, DATA ACCESS, AND RECORDS
As a condition of this warranty, you are responsible for properly using, maintaining and caring for your vehicle as outlined in your OWNER’S MANUAL and your NISSAN LEAF SERVICE & MAINTENANCE GUIDE, and maintaining copies of all maintenance records & receipts for review by Nissan. You are required to perform annual EV Battery Usage Reports at intervals of 12 months, 24 months, 36 months, 48 months, 60 months, 72 months, and 84 months. These EV Battery Usage Reports can be performed by a Nissan LEAF certifi ed dealer or any qualified repair shop facility. The 12 and 24 month EV Battery Usage Report will be performed at no charge to the customer, provided the work is done at a Nissan LEAF certified dealer. Any damage or failure resulting from a failure to have these required services performed, or that could have been avoided had these services been performed, is not covered under warranty.
You are also required to provide consent to give Nissan access to data stored on vehicle systems for the purpose of vehicle diagnosis and repair. Failure to do so is likely to result in denial of warranty coverage.
Evidence of the performance of the required maintenance should be kept and presented as proof of such maintenance in connection with related warranty repairs. To assist you in maintaining appropriate records, the maintenance log located in your NISSAN LEAF SERVICE & MAINTENANCE GUIDE can be used along with supporting repair invoices, receipts and other such records.
It's pretty bad that the dealer didn't honor the warranty without being told, but the fact that they didn't honor it even after you reminded them about it is really ridiculous.
Time to find another dealer.