A:AnswerWhat they mean is to use the phone and don't charge it until the battery level is below 30%. This prevents fires in case they crack the battery when removing it. It has nothing to do with Max available Charge in battery health.
A:AnswerMy understanding is that the battery has to be replaced by an approved Apple Service Tech to validate the warranty.
It is a mote point if you have Total Tech.
Service is free; battery cost is at a discount.