Does DJI recommend routine deep battery discharge for the P4P Intelligent Flight Batteries?

If so, how often and what is the procedure for doing so?

Only if the cell voltages don't match, take it down to 8%, then recharge to 100% the same day.
Avoid going much lower than 8%.

Only reference DJI make is to fully discharge and recharge the battery at least once every three months, at bottom of manual under maintenance in battery safety guidelines:-

https://dl.djicdn.com/downloads/ ... y+Guidelines+En.zip

I have seen some recommendations that after 20 recharges to do a deep cycle recharge. However, I have not seen any supporting research on the subject. I do a deep cycle when I remember to do one.

Before taking the battery on an airline flight, a fully discharge is recommended. More details, please check the battery guidelines in 3#.