There seems no way to have google maps api key free without credit card. To test the functionality of google map you can use it while leaving the api key field "EMPTY". It will show a message saying "For Development Purpose Only". And that way you can test google map functionality without putting billing information for google map api key.
<script src="https://maps.googleapis.com/maps/api/js?key=&callback=initMap" async defer></script>
~ Answered on 2019-05-19 17:21:16