16 automatic transmission 1.6 corolla ran for a period of time in d gear, and the voltage dropped by about 12.9, and it was about 14.3 when shifting to p gear. Is it normal?

Hello, this is normal. When the engine runs at idle speed or above after starting, the generator will supply power to the electrical equipment of the whole vehicle and charge the battery. In the P gear, the vehicle is in a stop state, and the electrical equipment is much less than that in the running state, so the voltage is higher, and many electrical equipment will be turned on when the vehicle is running, so the voltage is lower.