Does the car have to be running to use the car charger for my cellphone?

NO. Just make sure there is power there, may have to put the key on Acc, but the draw is very low, it does not need to be running

it will not charge the cell phone unless the car is turned on- look at your charger light- when you shut the car off, the light on the charger shuts off too, so it is NOT charging if that light is off- most GM cars are like that.

Oh the good old days of cigarette lighters. They ran w/o the key in the ignition. The plug in in the dash has to have the key in and turned to acc. I have not checked the rear plug in yet, and it my be the same as the front. Perhaps this helps in not burning the electronics of the vehicle out due to a bad charger shorting out or what is being used sending a reverse current to mess the computers up. My 2005 Buick had the plug-ins wired to be used all the time, running or not.

My 2017 Terran doesn't give me low feul signal when I'm running out of gas

GuruZ15H4, Not to be a smart ass, well I actually am, but, that is why there is a fuel gauge on the dash. When it gets to between 1/4 to 1/8 tank, stop and fill back up. My 2014 does signal "low fuel" when it gets to 1 to 2 gals left in the tank, but not before. That's cutting it way too close though. Perhaps there is a bad wire connection, a sensor not working, or you fill back up before it goes off. I think when you check your center display it will tell you you're low on fuel, but I am not sure if it lasts or not.

Where is the car charger located in a 2017 Terrain?

Where are the charging ports and the auxiliary plug in on the 2011 GMC Terrain slt-2?

Round one is in nook with a plastic covering and phone one is in box between front seats