How much is the battery cart service for these sights in Beijing?

Here is the info. I know:
I don't see the battery cart at BJ Zoo, and you can take the special view car to see the animals there. I remember the fare for the car is included in the entrance fee.

Old Summer Palace, it costs CNY6/person to have a round trip.

Temple of Heaven, there seems no battery cart. Neither is Tiananmen Square.

Battery cart in Jingshan Park costs CNY5 and Beihai Park's is CNY10 per person.

My friend told me that there are battery carts in Forbidden City, but we are not clear about the fare.