Suddenly cant charge 6s plus in car using USB

Recently noticing that when I plug my iphone into the USB port in my car, the phone's battery icon switches on & off; i.e. from charging to not charging. Using the GPS feature drained the iphone battery in a short period of time yesterday. Per phone battery stats, battery is at 83% max capacity and I'm using the same apple cable I use to plug into the wall & in the car.

Would really like to be able to change my phone in the car again - any suggestions are appreciated. Have already checked/cleaned connections.

Thanks!