As Google is a third party, they require you to sign up and provide your billing details in order to use their products.
Google provides a monthly credit of $200 for their Google Maps platform.
Read more information here
This normally covers map usage on your website, meaning the chances of you exceeding this limit are very low. We would, however, recommend setting a daily billable quota limit on your billable API.
That way, if your API usage reaches the billable quota limit on any given day, your application will not be able to access the API for the remainder of that day.
This will simultaneously ensure that you are not billed for the maps module on your website.
Click here to view instructions on how to set a quota limit.